They're super, super easy. All you have to do is measure, glue the binding onto the tank using aquarium silicone, cut the mesh pieces to size, and slide them in. Very cheap and VERY easy. The hardest part is usually tracking down the materials. I found the plastic needlepoint mesh at Michael's craft store, and the plastic report cover binders at Staples.
I definitely agree with the others' statements about tankmates. Unfortunately five gallons isn't enough space for small schooling fish. These are very social animals that swim in schools of hundreds to thousands in the wild--keeping only two or three by themselves isn't very humane from an enrichment standpoint, and many need lots and lots of space to exercise and express their natural behaviors.