How do i share my model

If you want to share model please perform these steps:
1. Click "My models"
2. Click on the model name you want to share
3. You'll get "Model details" screen
3. Click yellow button "Share model"
4. Add a person

"Sharing" screen shows you what you are currently sharing and invitations. 

Do you have to have a license to receive a share.  If they only can view it do they need a license?

No, you can share your model between users in the Free account plan. The only limitation is that you cannot accept an invitation to the model that exceeds your account plan limitations. In such case you'll need to switch your account to a paid account plan.