Datastore is basically just a service used to store data to a server, which can then be accessed later by a user at any of the places in your game.
Of course, you probably already knew that, so here are a few simple methods you can start off with:
##Getting the Datastore
local DataStore = game:GetService("DataStoreService"):GetDataStore(name)
The name parameter is pretty self explanatory. It's just the name that you set for your Datastore, and the way you access it later on.
This is the base method that is always required in fetching the datastore in order for you to use it. This is generally at the start of the script.
##Saving Value to a Datastore
DataStore:SetAsync(key, value)
Key is a unique string that the service uses to fetch data for the user or the world. For use with saving individual player data, you would want to use the player's ID as part of the string
Value is simply what you're saving. This can be a number, string, boolean, or a table.
##Getting Value from a Datastore
DataStore:GetAsync(key)
Key is the same thing that you used in the SetAsync method. When you use this method, it will return the value previously saved in the datastore with SetAsync.
Now, you'll probably need a bit more explanation than this, and there are some great resources you check out, including the Roblox Wiki
I would also suggest checking out some other resources such as Youtube. Here's one video that may help.
Anyways, I hope this helps. If not, or if you have any further questions, please leave a comment below, and I'll see what I can do to help.