Hi Gheorge
There has been literally hundreds of posts in this forum on soldering. Too much to repeat. Put “soldering” in the search filter and prepare for some reading. You might be ready in about a week.
Those header pins are quite large and if you plug them into a breadboard the extra heat sinking might be a bit much for a 25W iron. It would probably need about 20 or 30 Sec of recovery time between soldering pins without the extra.
You haven’t mentioned an important component - what solder are you using? 60/40 (approx) resin core is best - lead free will be much harder to use, and harder to tell when you have a good joint. Cheap imported solder is very variable - it’s worth investing in a brand that you can rely on.
The best way to find out how to do it is to practice, and compare your results to the information available on-line.
When the solder melts quickly if you touch the end of the roll to the tip of the iron.
Just a few. Take a guide from the on-line videos. The moment that the solder wicks into the pad and the header pin (whichever comes second), creating a smooth conical shape is the moment that the solder has worked. Notice that there is a short pause after removing the solder, and a similar pause after removing the iron to ensure that nothing moves while the solder is hardening. Practice.
Again, the examples will be a good guide. The devices are quite sturdy enough for a typical solder job.
You can’t clean the tip too often. Definitely after each pin, to start with, because you will be pausing. Experienced solderers will do all pins in one go, but any pause needs a cleaning. I find that a ball of copper strip is best. You will get into the habit of just dabbing the hot iron into it a few times each time you remove it from the stand or replace it in the stand.
Be careful about mounting the module firmly - you don’t want it to move while you are trying to bring all the components together. I like to insert the male long header pins into a short length of female headers (don’t use the breadboard!) so you have something substantial enough to mount in a small vice, then position the module so it sits down properly on the short pins. I have noticed that sometimes these header pins are difficult to solder if they aren’t abraded with a sharp blade - practice will tell you how easily the pins take the solder.
It looks like Jeff has covered your questions to help you get started.
My advice is spend as little time with your soldering iron on the board as possible but take all the time you need to ready yourself between soldering the pins.
If a solder joint isn’t looking the best you can always try and reflow the joint again after its cooled down.
