Explain to me this whole konosuba situation!!!?

I loved the anime, then found there was manga and light novels. I planned to get these. After that, I had been sure that I had read everything (except from the web novel) I had THOUGHT that there were two spin off novels: Gifting this wonderful world with blessings! and Gifting this wonderful world with explosions! But now I find out that there are 11 volumes of the former! Are they the same seiries with a different name, are they an altered version of the original? Are they just more stories? Please tell me what I need to buy in order to have completly read konosuba!! Because I am CONFUSED.