Enter pico in response to a shell prompt and use pico's fine, self contained "help" feature to learn all about pico.  Pico will start by drawing an empty editing window on your screen, like so:

Once you see this screen, your keystrokes are no longer going to be accumulated by the shell for interpretation as commands.   Instead, each keystroke you type will go to pico and all the "ordinary" keystrokes will show up in the window as text (unless you hold down the "control" key on your keyboard).  Once you start pico and start typing, the window might look like so:

In pico's on-screen documentation, the ^ symbol is used to mean "hold down the control key while simultaneously typing the following key."  So on the pico editing screens, above, you see  at the bottom of the screen a bunch of reminders in inverse video like ^X Exit    Holding down the control key and then pressing the 'x' key will cause pico to exit.  (Pressing the 'x' key without holding down the control key will just enter a text 'x' into the text editing portion of the pico window.)  Note:  In the pico display of ^X Exit , that's a capital X after the ^caret.   To me, that would indicate that you should hold down both the control key and the shift key before depressing the 'x' key.  But the "shift" is unnecessary.  I would have made that pico display look like ^x Exit , but pico doesn't — I don't know why.  Anyway, the two most important pico control keys are:

• ^X  which exits (quits) pico and takes you back to a Unix shell prompt.  (Note:  pico is user friendly, unlike some other Unix programs.  If you've entered or altered text in pico, as I did in the second figure, above, pico prompts you for a file name to save your entered text into before it exits.)
• ^G which brings up the first of a series of on-line help screens, which, among other things, explain what all the other control keys do in pico (Note: Other programs may [usually do, in fact] interpret control keys differently than pico does.  Each program is free to chose its own conventions. Sorry.)

To start editing an already existing file with pico, just enter  pico file_name.  If no such file exists, pico will create a new but empty file for you by that name and then start with an empty editing window as shown in the first figure, above.  But, as noted above, you can also start pico with no file name whatsoever and it will wait until an appropriate time to ask you what name you want to assign to the new file it will create for your text.

I think I've given you enough information here to get started, and pico is simple enough and has a nice internal help system; there's also a quick reference card.