Sometimes we want to get information about something. Is it Wednesday? How many people have signed up to attend the event? Which channel is your favorite? Asking the question doesn't change anything. It's either Wednesday or it isn't, and asking the question doesn't make it Thursday.
Other times, we do something to the world, and something changes. We throw something in the trash. Now the trash can has more stuff in it. We buy a drink. Now we have less money.
One or the Other
In many software systems we try to keep a clear separation between obtaining data and changing things. When we're asking about something, we don't change things, and when we change things, we don't get information back. If, when we've told the system to change, we want to know whether or not anything actually happened, or what the new situation is, we'll have to go ask.
These exercises focus on these two types of operations.
Go make up more
... and submit pull requests