When should we use rather?
Rather means two things, depending on context. If someone says "I would rather talk than read" for instance, it means they want to talk more than they want to read. Talking is preferable to them. Similarly, if you see in the movies that someone says "I'd rather die than give up!" or "I'd rather die than tell you what you want to know," it means the same thing: they would rather be killed by the antagonist (bad guy) than do what s/he wants.
Rather could also mean "an amount" or "to a degree." It's used to modify things. "He is rather nice." Here, rather is modifying nice. It's most literal meaning is "somewhat" i.e. "He is somewhat nice." or "kind of" "He is kind of nice." However, because English is weird, the word "rather" is often redundant. People will often say "He is rather nice" and mean the exact same thing as "He is nice."
(Just a quick note or two that I noticed in your question: "I had" means something I did in the past, for example, "I had gone to the store." This is used usually when telling a story. "But Joseph had already told Sally he loved her." Or it could mean "I possessed." E.g.: "I had a book, but I lost it."
Also, the proper word you're looking for is "than," not "then." Then is something used to indicate time. "I ate lunch, then I went home." Than is used with rather. "I would rather die than..." It's confusing, I know, because they usually sound very similar, but it's just something you'll have to remember. To be fair; however, there are some English speakers who don't know the difference between then and than!)
1. More readily; preferably: I'd rather go to the movies.
2. More exactly; more accurately: He's my friend, or rather he was my friend.
3. To a certain extent; somewhat: It's rather cold out. I was rather hoping you'd call.
4. On the contrary: This is not a thoughtful criticism. Rather it is an insult.
5. (ră′thûr′, rä′-) Chiefly British Most certainly. Used as an emphatic affirmative reply.