Assembling charms can be confusing but that is only because there are several types of attachments. Some are made so that charms can be easily slipped on and off - you can then ring the changes with different colored charms and so on or wear your bracelet plain and simple if you like.
The kinds of attachments you will find are
a. Jump Rings
Jump rings are used to solder a charm to a bracelet and are a permanent and secure solution for fitting a charm but getting each charm added in this way can prove expensive as you may be charged for attaching in this way. This is especially the case if you want to add 10, 20 or more charms to your bracelet. Another disadvantage of this method is that it does not allow you to "ring the changes" which is part of the beauty of a charm bracelet.
b. Split Rings
A split ring is exactly like the spiral ring you find on a keyring (although obviously much smaller). You push the charm onto the ring and it opens so that you can thread the charm onto it then it closes so that the charm remains secure. They are quite fiddly to work with if you have small delicate jump rings, but they do mean you can fit charms yourself without having to go to a jeweller. Also as the metal is quite thin they are better with thin bracelets as stretching the split ring too much can cause it to remain open and less secure. You can help that by "tightening" the ring with a small pair of pliers.
c. No Solder Jump Rings
These are high quality jump rings which are cut in such a way that they can be opened and closed with pliers to give a neat close which is secure yet does not have to be soldered. This means that the charms can be moved at a later date - although it is not an easy option for changing your charms for a night out!
d. Lobster Catch
A lobster catch is the kind of fastening you find on necklaces where the ring is opened and closed by means of a small tag which is pulled to open the ring and released so that it springs back to form a closed and secure ring. These are the easiest attachments to be able to quickly change your bracelet.
If your charms do not come with attachments, then make sure that you buy the necessary pieces at the time of ordering to avoid the frustration of getting your charms in the mail and not being able to wear them. If you buy charms at a jewelry store ask for them to be fitted at the time you buy them.