Your home directory is likely /home/username and can be seen by using "echo $HOME"
When you initially log in you are located in your home directory.
The shell sees ~/ as equal to $HOME
Therefore "cd ~/Downloads" is the same as "cd $HOME/Downloads" and is the same as "cd Downloads" when you first log in.
Any time you have changed the directory you are currently in you can see where you are with a simple "pwd" which will display the present working directory. You also can always return to your home directory with a simple "cd" with nothing following.
The command "ls" displays the content of the current directory and thus you can see what is located there.
Use the man pages to see how ls, cd, pwd, echo, and almost any other command function and are used.
A simple
bash tutorial will assist tremendously in learning how to navigate and manage the system.