I'm am trying to clean/edit shape files that were created by algorithm in Qgis. My problem is when I try to split some polygons,they have invalid geometry. Is a way to identify these error maybe in a different colour for me to fix them?
You can use Topology Checker plugin. With it you can set topological rules and highlight where the problems are. Check the documentation here.
Some error can be corrected by some processing tools. Please check this Faunalia videos: