Copy a mesh into another

Hi, i made 2 diferent objects from 2 separate cubes. i want to know if theres a copy & paste instruction to copy the whole mesh from one object to the other? i don’t want to model it again from scratch in the edit mode of one of the objects. the problem is that i want to place one object into another so when i enter edit mode i can edit both at the same time. is it posible?

thanks in advance…

Select both objects hit ctrl-j to join them then you can edit together.