Aligning objects by face? Aligning vertices?

I am totall ynew to Blender … reading myself through tutorials and watching tutorial videos, I so far managed to create a nice little gun tower, consisting of two objects atm … a central body and the two attached guns as a second object. The two started out as a larger cube and a smaller cube glued to its side. But: I just went into the front view (1, then 5 on numpad) to align the smaller cube to the large ones side by hand. How can I do this perfectly? ALl I can imagine at the moment is to join the two into one mesh, then select the vertices of the cube sides to put together and use some scale by axis 0 command and then to separate the two objects again. But is there no simpler way to just stick two faces together?And while I am at the “s[yxis]0” command to align two or more vertices: Can I somehow define one as unmovable? If I have two vertices, and one is exactly where I want it, how to I bring the other down for instance (z axis) where the other is at, without changing the correct one’s position?

Your post is a little unclear since you don’t show us what you have and what you want to achieve.

I recommend to experiment with the snapping tools

Will read on. What I’m trying to achieve is just this: Slap two faces together with 0 distance between. Just imagine two cobes and I just want them side to side, glued together … aligned.

In a more complex situation: Align a gun object perfectly to its turret etc.

Snap to faces and Align rotation with the snapping target.