How can I get vertices,faces, or edges to align with other meshes?

Hi, I’m sorry if this is a newbie question but I for some reason can’t find out if it is possible to get two meshes to align together.

For example if I have one square mesh and make it into a floor how would I make another cube lay directly on top of the floor so they dont go through each other?

Thanks in advance for anyone who replies.

Switch to face snapping mode (ctrl+shift+tab, or snapping options on the 3d view header), select the cube, G to move, Z to lock the Z axis and holding down ctrl point to the floor.

Could also put the object origin to the base of the cube and then use a floor constraint to keep the cube going trough the floor when moving it.

the most common way is just to zoom way in and adjust it manually