Straight cuts: Make a 0-degree cut through a stack of two pieces of 1×4, edges to the fence. Butt the cut ends together, with the same edges against the fence. If there's a gap, adjust the saw.
Miters: Make a 45-degree cut through two stacked pieces, edges to the fence. Mark these edges and put them against a square, as shown. The cuts should mate perfectly.
Bevels: Cut a 45-degree bevel through two pieces set on edge, faces against the fence. Form a corner against a square to see if the cuts mate.