Wonderful day! Looks not bad, but doesn't look perfect, sorry. Yet, there's progress it seems!
Generally:

1. Clean both platforms for the join, and the soldering iron;
2. If the solder does not come with flux, apply a proper flux to the both ends (flux must be compatible with the metal);
3. Heat and apply a solder to the first fluxed end;
4. Heat and apply a solder to the second fluxed end;
5. Heat and join to ends together;

I've been into electronics for almost two decades, and I relatively recently noticed the following video that you may find interesting. It is more modern than books and quickly summarizes the principles to be researched manually further if required (e.g. in books):
- Do This Before You Solder Anything

I believe it mostly comes with practicing, and experiments with an iron that has a temperature indicator should support it.

// Image source