You'd probably make your life a little bit easier if you read the man files. try:
Every user had a UID. thats just a number.
Each line is a separate user. Linux maintains quite a lot of user accounts, so don't be surprised if its a big list.
the data is colon deliminated. The third entry is the UID. The fourth is the GID. By default linux assigns the same GID and UID to each user.
Basically it simplifies to this. There are nine catagories of access. (there is actually some more complicated stuff but start with the basics).
There are three access types:
There are three access specifications
with each file, you can specify who owns it, what group it is in, and these 9 access permissions
This should list the file permissions. This is what it might look like.
-rwxr-xr-- 1 user group 0 Dec 10 22:27 your_file
Of the first ten characters the last nine represent the values the first tells you what kind of file it is. - for a regular file d for directory, there are a lot more. Outside the scope.
Those last nine are telling you that the user by the username of "user" had read write and execute access to the file
Anyone who belongs to the group called "group" has read and execute access to the file
Everyone else only has read access.
That's basically what you have to work with. Simple access permissions are structured based off of this.
Hope that helps.