Standard metal bunk beds conform to the same basic design specifications. They consist of two end pieces, a platform--usually some kind of grille--for each bunk, cross braces and connection hardware. Many also come with additional bells and whistles, such as an independent ladder or decorative touches. When in doubt, consult the assembly instructions that came with the bed.
Set the end pieces up approximately where they will be when the bed is assembled.
Install the cross brace for the top bunk on the side closest to the wall. This usually connects via a tongue-and-groove arrangement. Install the three remaining cross braces in the following order: bottom farthest from the wall, top farthest from the wall, bottom nearest the wall.
Tighten down all connection hardware for the cross braces. If your model uses connection hardware that includes both the cross braces and the mattress platforms, skip this step.
Install the top bunk and crash barriers. The specific method for this varies. Consult the assembly instructions if you have them. If you don't, examine the bunk and have a plan before you pick up the platform.
Install the bottom bunk. This is almost always done via the exact method used to install the top bunk. Tighten down all connection hardware for both bunks.
Not all kits require all the tools mentioned above. Some kits come with an appropriately sized Allen wrench. Consult your assembly instructions for the exact tools needed for the job.