Meaning : Get people together.

Example : Assemble your colleagues.
Get together all those who are interested in the project.
Gather the close family members.

Synonyms : assemble, gather

Meaning : Get together socially or for a specific purpose.

Synonyms : meet

Meaning : Work together on a common enterprise of project.

Example : The soprano and the pianist did not get together very well.
We joined forces with another research group.

Synonyms : collaborate, cooperate, join forces

Meaning : Become part of. Become a member of a group or organization.

Example : He joined the Communist Party as a young man.

Synonyms : fall in, join

Meaning : A small informal social gathering.

Example : There was an informal meeting in my living room.

Synonyms : meeting