Hello and welcome. Some metals can be joined just by fusing, but for most of those we use, hallmarking quality solder is required. Soft soldering with a hot iron is a definite no no.

I would suggest you look at Andrew Berry's YouTube channel for an introduction, maybe starting with this:
https://www.youtube.com/watch?v=NXPMxgIVDJU.
For most purposes start by practising with strip solder (easy, or hard) on copper, which is a cheap option. Dennis.