How do I thin out my hair WITHOUT thinning shears or going to a hairdresser?

I have really thick and curly hair and I had already straightened it because I thought it would look better that way, it does for the most part but it's still really thick. I was told that I should thin my hair out but I didn't quite know what the difference was between the two and I still don't really know exactly so if someone could explain that to me then that would help a lot. I don't want to use a razor because it sounds really time consuming and I'm not even going to bother buying thinning shears unless it's strongly encouraged but I'd appreciate it if someone thoroughly explained to me how to thin out my hair with plain old hair scissors.