Guidance needed removing lines from a CSV

I’m new to Powershell, but not scripting. I had a project dumped on me. Merge some CSVs and remove unneeded lines. I’ve been trying to find resources on this for about a week. Everything I find is a good bit over my head. In Visual Basic I can delete lines by character count, and am familiar, but every PS tutorial I find is reading by delimitation, and if it is not, I can’t understand the syntax. I am unfamiliar with the commandlets. I need a quick and dirty way to delete (for example) line 5 and 7 form a comma delimited CSV.