Tries are some kind of rooted trees in which each edge has a character on it. For a bunch of strings, their trie is the smallest rooted tree with a character on each edge and each of these strings can be build by writing down the characters in the path from the root to some node.
This is a nice tutorial for tries - Trie (Keyword Tree) Tutorials & Notes
After reading this read this amazing tutorial here for tries on bits - Tutorial on Trie and example problems
Solve these problems now -
Problem DISUBSTR (classical)
Problem SUBXOR (explained in the blog)
Codeforces (also explained in the blog)
Codeforces (also nice)