Cut pipes using pipe cutter and deburr.
Clean the inside of fittings, and the outside of pipe, with wire wool, or a cloth or tool designed for the job. Cleanliness is important!
Join pipework together with fitting(s) to make sure it all fits.
Disassemble.
Use a brush to apply flux to the pipe ends and reassemble pipework, (good idea to twist the fittings on so flux is spread evenly inside).
Remove the excess flux from the outside of the fittings which prevents the flux sucking the solder outside the fitting.
Position a heat-proof soldering mat behind the fitting.
Heat the fitting not the pipe and try and get used to when it gets hot enough. If the flame goes green it’s just gone over, and your joint may oxidise, go black and not stick.
When you think it’s hot enough, apply solder (or if solder ring, watch ring appear), and it should melt and be pulled into the joint. Remove heat and let it cool gradually then wipe with wet cloth.
Biggest mistake beginners get is not having a suitable flame not positioning it right and not knowing when to stop. Do a few practice runs then cut joint apart and check for penetration. Joints must be pushed right home to the end to be successful. Overheating is a common cause of leaks.
If using endfeed a 15mm length of solder does 15mm pipe 22mm of solder does 22mm pipe.
Remember to use lead free solder on all potable pipework though you can use leaded or unleaded on CH plumbing.
Please note that you cannot solder a pipe if there is water present as the pipe temperature will not get hot enough to melt the solder.