To "share" means to let other people use something that's yours or that you're using. Usually, when we use the word "share", we follow it with two pieces of information: what you shared, and who you shared it with.
She shared her toys with her brother.
But you can also just use "share" like this:
Let's share it.
Or even like this:
We have to share.
In the last example, the thing that you're sharing and who you're sharing it with must be understood based on the situation.