I always melt the solder with the soldering iron or soldering gun.

With a small ammount of molten solder attached to the soldering tip, I touch this molten drop to the joint. When it has heated the components suficiently the solder flows and complets the joint.

If more solder is needed, touch the solder to the tip briefly 'till the joint is filled out.

With a low power soldering iron You must use small diameter solder.

Rosin core is traditionally used, but any non corosive flux will work.

You may need to retinn your soldering iron in order to get maximum heat transfer. If the tip is not too dirty you can clean it with a wet sponge and reapply solder. If the tip is really dirty and pitted you will need a file or fine sandpaper to clean it.