I got into soldering as a child, but never learned how to do it properly. Years later I found this comic-book-style guide somewhere online, which made it quite easy to do without messing it up: https://mightyohm.com/files/soldercomic/FullSolderComic_EN.p...
Important to note that these days you really should use lead-free solder. You'll find all sorts of people going around claiming that leaded is better, but it's really not, and it's not worth the health risk. Your iron needs to be about 20c hotter than for leaded and your solder joints will look dull instead of shiny. If you find lead-free solder to not flow properly to be grainy your iron isn't hot enough.
Still wash your hands after using lead-free solder by the way. You don't want to be eating rosin or copper either.
Copper is an essential trace element for many living organisms, including humans, meaning you need copper to survive. Generally, copper has low toxicity. (That is, unless you have rare genetic defects such as Wilson's Disease)
Lead is nothing like that. We don't need lead to survive, we shouldn't put lead in our bodies. Lead is also known to accumulate in your body (especially your brain). Avoid lead exposure as much as you can.
Still wash your hands after using lead-free solder by the way. You don't want to be eating rosin or copper either.