How do I teach my 2 year old to share?

To be honest, I don’t teach my 2-year-olds to share or be nice. These are difficult concepts for older children to understand; it’s not realistic for 2-year-olds. Partly because they are very ambiguous ideas – especially “be nice.” If every one of us answered what that was to us, we’d have that many different answers and ideas.
Instead, I focus on “taking turns” and on “kindness.”
Yes, kindness is ambiguous, but it’s less so than “nice.” Kindness is about your actions towards the other person; “nice” really comes down to doing what someone else wants you to do to please them. I want my children to be kind, I don’t so much care if they’re ever nice. Kindness means you don’t grab from someone; you use your gentle hands to touch them. If the child is capable, it means using her words to tell them her feelings.
I fully expect to be actively involved in the play relations of my 2-year-old. I let them play alone, but I am ready to “engage to disengage.” Meaning, I pop in to help problem solve or resolve conflicts and then I pop back out and let the play continue.
Taking turns is a precursor to sharing. Sharing comes from a genuine heart, but property rights must be understood before sharing can be genuine. I can only share what is mine. I can loan you my pan, not my neighbor’s. And, as adults, we don’t share everything.
For example, I might share my husband to mow someone’s lawn, but not for everything. The idea that we share everything is just not teaching a real life skill; it’s more about being nice and keeping everybody happy. Yes, with taking turns, children sometimes cry. That’s the risk, and this is where real life is taught. If someone is playing with a toy, he gets to play with it until he is done. If my child wants it, she gets to ask for and wait for her turn. I will make sure she gets the next turn, I will also comfort her while she waits. But wait she will.