Below is a brief note about two kinds of capillary joints found in plumbing:

When you look on the shelves of your local DIY store, you will see two types of capillary joint, one is the ‘Yorkshire’ or (integral-ring joint) and the ‘End-feed’ joint. Yorkshire joints are self-soldering, with a small ring of solder already inside of the end of the fitting, and just needs to be heated with a blow torch. End-feed joints, on the other hand, do not contain solder and are plain and smooth inside, so you need to apply solder wire to the hot joint. Yorkshire joints are slightly more expensive than end-feed joints. But you should have no trouble with them. Hampstead Plumbers use these joints.

Yorkshire joints.
Thoroughly clean the end of the pipe on the inside of the joint with wire wool. Smear a little flux paste inside the joint and on the end of the pipe. Assemble the joint, making sure the pipe is pushed home firmly. Make a small mark with a pencil so that you will know if the joint moves. Heat the joint and pipe with a blow torch until you see a small, fine, silver ring of solder appear where the pipe enters the joint. Use on an extra bit of solder if you think it needs it. Allow to cool off before moving. A Hampstead Plumber uses this type of joint.

End-feed joints.
The process is almost the same as above, using solder and marking in the same kind of way. You’ll know when the temperature is right because the solder will immediately melt and flow like water on the joint. When the temperature is reached, continue to dab the solder into the joint until you see it start to gather at the bottom of the joint, but do not use so much that it drips. Always allow the joint to cool fully before moving.
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