If you are a beginner, you don't need to pay attention to this at all.  Even people who skate for a very long time usually don't even look at this.  But it can still be useful to have some knowledge about it. Wheelbase says something about the distance of the trucks, and that affects the turning circle. A shorter wheelbase makes turns sharper. A larger wheelbase makes your ride smoother.

What discipline you are going to choose can affect your deck choices. 

- Street, park 

Usually between 7.5 to 8.5 

- Pool, mini, vert

For this, you usually want to go a little bigger than what you would normally go for. 8.5 and above or old school pool decks 

- Freestyle

For this you often see that they have some smaller decks usually between 7.25 - 8 besides that they are also usually a bit shorter in length (You also have specials old school deck for this)

It's really about personal preferences. There is no wrong choices you can make. 

Mellow

Most decks have a mellow kick. A mellow kicktail is more relaxed for street tech skater because it is more responsive and you will change your foot position more often. If you're just starting out, we recommend trying a mellow kicktail

Steep

Steep kicktails give you more pop, but it also takes more effort to pop so you can get exhausted faster. With a steep kick you do have a better feel for where your foot is on the deck which can be useful in a pool, mini, vert.

It is also a matter of personal preference, and you cannot make a wrong choice here.

Decks come in all kinds of shapes, some more practical than others. Here we discuss the three shapes that are most common. There are also differences in the shape itself. 

(shapes within shapes a.k.a shapeception)

Popsicle.
This is the most common shape in skating. We recommend starting with a popsicle, which is ideal for street skating and transitions. It looks like a symmetrical deck, but the nose is usually slightly larger than the tail. The nose should be bigger so that the foot has a better grip when ollieing. Besides, it also makes the nose heavier, which would make the ollie easier (because the heaviest point goes up first) and the rest follows. The tail of the skateboard is smaller and slightly closer to the ground, making it more responsive when popping.

Old school
A classic deck from the 70s. These kinds of decks are still very popular and are more often used in pool, mini or vert, but you can definitely use them in the skate park too. The old school shape always comes with a square/fish tail. The nose can vary, some have a shorter, flat nose (single kick). But you also have them in Double kick

They used to come with flat or almost no concave, but nowadays you also have them with a modern concave. The shape has its advantages and disadvantages with certain tricks

Shaped
A shaped deck is difficult to describe because there are so many variations of it. But each shape is designed for a particular purpose in mind. (Which might be a bit harder to do on a popsicle) 

If you choose a shaped deck, it may take some time to get used to. Once you get the hang of it, this might be the shape for you. The downside is that when it's time to buy a new deck, you have to look for the same one. Which can sometimes be tricky because they are made less frequently and it is sometimes difficult to get the same one.

All these choices are skateable. no wrong choices you can make.

As a beginner, you don't need to worry about this, but try to choose one with medium concave so you can use it as a starting point. (Most beginner completes have a medium concave)

 If you are more advanced, you will definitely notice the difference in the concave.

 These are the three most common concaves:

Low concave gives more stability but is harder to flip. 

Mid/mellow concave is the most produced concave available. It is a perfect balance between low and Steep/high concave.
This gives you the stability you need and is high enough to flip well with it.

Steep/high concaves flip much easier, but are also less forgiving than medium or low.If you flip it too hard,
the deck can over-rotate.It may also be more uncomfortable for some because the edges are slightly
higher and you may notice this on your feet.

But as with anything for a skateboard deck, it is your personal preference.
There are no wrong choices.

A wider deck gives you a bit more stability. Which is useful for pool, vert and mini riders. 

Narrow decks can be especially chill for flip tricks or freestyle skating, as they are a bit lighter and therefore rotate faster and easier. 

It is important to base the choices on what you want to do. 

That is hard to determine for someone else because it is a personal preference. But there are some factors why a narrower or wider deck may be more relaxing for you.

The size of your foot can influence your deck choices.  Since for smaller feet, you don't want your deck to be too big. That can make certain tricks more difficult.

We recommend if your foot size is around 42 to get an 8.0 deck.  If you have a smaller foot size  around 37, I would go for 7.5. At a shoe size 45+, I would consider going for an 8.5. (It's normal if your feet are wider than the deck itself)  (42, 37, 45+ EU sizing)

For children up to 12 years, there are also special children's skateboards. These are smaller and are called Mini or micro 

What we recommend here is a suggestion. Nothing is wrong! It is mostly about personal preference.

For beginners, we recommend buying a complete deck and upgrading parts from there as you get better. A complete deck is all you need to get started. Buy it and go skate! completes often come with softer wheels, which makes riding a little more comfortable and easier. 

As a beginner, you should pay particular attention to the width of the complete deck. 

 We recommend if you have a shoe size around 42 to go for an 8.0 deck.  If your shoe size is around 37, then a 7.5 is suitable. With a shoe size of 45+, 8.5 is the best to start with. (It is normal if your feet are wider than the deck) For children under 12, there are also special children's decks available, which are smaller called Mini or micro. 

But for personal advice, it's better to stop by the shop (Maanweg 24 The hague in the Netherlands) or contact or customer servers.