I wouldn’t bother with fertilizers for a beginner. Simple plants like Amazon sword, Java fern, Java moss, cryptocoryne, and duckweed (floating) are basically zero maintenance. Just plop them in the substrate and preferably have a light over the tank and they’ll grow. A note about crypts— they might appear to “melt” when you first put them in, but don’t throw them away! They will grow new plants from the roots and, once settled, will send out lots of runners to make free plants for you. I constantly find little baby ones around my tank, which I can stick in the substrate and have a whole new plant in a few days.