You've gotta read Lou's articles that Mannie linked to above. That's the first step. Second is to disassemble, clean, inspect and reassemble each kit fp section you've done so far, and every one you do in the future. It's cleaner and easier to do it before you ink them the first time. But necessary in any case. It's all in the articles, but the high points are that the nib must have a nice smooth tight fit against the feed, and the feed must end at the right spot under the nib. The section must fit well enough to keep them that way. If a given combination of nib, feed and section don't fit right, swap around parts till you get one that does. But don't bother assembling and inking a section unless it fits right, looks right and don't wiggle around after you put it together. I try to do fountain pens in groups and just put all the components of the sections together in a pile, and assemble them, disassemble them, fiddle around with them, and otherwise enjoy playing with them till I get enough that work together correctly to ink them, put them in the pens I have, and test them. Then the ones that do work get disassembled individually, cleaned and reassembled for storage. The ones that don't write well get disassembled, cleaned and go back into the box till the next time I feel like messing with them.
Specific problems with a given component may be fixable, or they may just need to be junked. But never just assume that because a section came with a kit that it must go into that pen, or that it will work automatically. Spare components can be ordered from several sources, so have some spares.
And remember, This is the fun part! So enjoy it. PS, it's more enjoyable if you aren't going through ink in $.50+ cartridges while you fiddle around getting things working, so go to staples and get a bottle of parker "quink" to experiment with and save the expensive stuff for demo's. But don't try to use india ink, artists ink, or iron gall ink, or the cartridges that come in the kits. only ink specifically made for fountain pens.