&& is the and operator so we use it to basically run two commands at once
& is a background operator, meaning say you run a command that takes 10 seconds to run, normally you wouldn't be able to run commands during that period; however, with & that command will still execute and you'll be able to run other commands.
and $ is something we can use to define enviornment variables for us like maybe a target IP or so instead of remembering it and writing it again and again .These are variables set by the computer(you can set them yourself but we'll get into that) that are used to affect different processes and how they work. Meaning that if you edit these variables you can change how certain processes work on your computer
You can set them by just easily doing export <varname>=<value> will set that as an environment variable
The | operator allows you to take the output of a command and use it as input for a second command.
It is worth noting that not all commands support the pipe, and some that do support it require you to use - instead of input, for example cat -
; command is basically the same as && but in this case its okay even if our first command is not found it will still run our second command
This brings us to mkdir, occasionally you'll want to make a new directory to store files in, and that is done using mkdir, the syntax of mkdir is mkdir <directory name>
ln is a weird one, because it has two different main uses. One of those is what's known as "hard linking", which completely duplicates the file, and links the duplicate to the original copy. Meaning What ever is done to the created link, is also done to the original file.
find is an incredibly powerful, but incredibly simple command. It allows you to do just as it says, find files. It does this by listing every file in the current directory, so if you ran find /tmp it would list every file in /tmp.
The true power of this command though comes from the parameters you can provide it. You can use find dir -user , to list every file owned by a specific user; you can use find dir -group to list every file owned by a specific group. The sheer customizability of the command is it's most powerful feature.
Every binary you execute on linux, is a process while it's run. A process is just another word for a running program. A list of user created processes can be viewed with the ps command.