Different Types of Locs
There are actually quite a few different kinds of locs hairstyles:
Sisterlocks are more like microlocs; they're very small and the installation process is very time-consuming, so you'd be better off going to a professional to get them done. Because of their size, they're pretty versatile and easier to style since they mimic small hair strands. For this style, you should expect to have to retighten every four to six weeks.
Traditional locs, on the other hand, are standard-size locs that are usually no bigger than a medium-size box braid. The upkeep on these isn't super involved, which is why they remain one of the most popular kind of locs.
As for freeform locs, these are locs that are created naturally, as in you'll have to clean and wash your hair as you normally would, then let it loc up over time. They require little twisting or manipulation and are probably the most low maintenance of them all.
Two-strand twist and interlocking locs are almost more to do with technique than a style of locs itself. The former can be used to start traditional locs (but do bear in mind that these tend to look bigger and frizz up a tad more easily). The latter uses a "pull-through" method where you take the ends of your hair and pull it through the roots of the loc using either your fingers or a tool similar to a crochet needle. You can pull it through up to four times going north to south and west to east to keep the knot firmly in place.