To be equally involved in something; to work together.
You can't do all of this work on your own—why don't we go shares?
share and share alike
To take or distribute equal portions or shares of something.
When he won the lottery, Dan gave part of the money to every family in the neighborhood. "Share and share alike," he said. Come on, kids, there are enough toys for everyone to play with. Share and share alike!
do (one's) share
To contribute work to that of others in a group. If you don't do your share with the slides, our presentation will never be finished on time. We haven't asked you to do anything extra. Just do your share.
lion's share of something
Fig. the largest portion of something.
I earn a lot, but the lion's share goes for taxes. The lion's share of the surplus cheese goes to school cafeterias.