Metal bed frames vary by size and specific design, but assembling them is usually fairly straightforward. If you don't have specific instructions for your metal bed frame, use this as a basic guide.
Set the two bed rails down on the part of the floor where you want the bed to go.
If your metal frame has headboard brackets, connect them to the top end of each bed rail using bolts or screws.
Lock the cross arms together or attach the cross rails using bolts or screws. There should usually be at least three cross rails: one at either end (forming the frame) and a third in the centre (to stabilise the assembly). If your metal bed frame involves cross wires, pull them diagonally across the space between the two bed rails and affix them to their appropriate slots. Test the bed's sturdiness by stressing the points where the cross rails meet the bed rails. Lock in place, and check for bending or wriggling.
Measure the frame with a tape measure to make sure the mattress will fit comfortably inside the rails. If the measurements are off, this is the time to make corrections.
Snap the casters, wheels or glides into their appropriate brackets. The specifics will vary depending on the particular type of bed you have, but they all should be securely locked to the brackets.
Secure the brackets to the four ends of the bed rails using bolts or screws. Test them by placing stress on the contact points, to ensure they will support the weight of the mattress.
Attach the headboard to the headboard brackets, if appropriate.
Place the end caps on the ends of the bed rails. They will keep the sheets from snagging on the metal.
Place the mattress on top of the assembled frame.