Haha, that's a bit tricky, because it's often done wrong by (southern) Germans, and because you're actually describing two ways of using "als".
1. The rule for "als" and "wie" is actually pretty easy: "als" is "than" and "wie" is "as" when you're putting things into relation: "bigger than" = "größer als" vs. "as big as" = "so groß wie". The problem is that many people in the south say "wie" when they should be using "als", which is confusing. I think you're in BaWü? Then just use "wie" when in doubt, fully knowing you might be wrong, and you'll fit right in ;-)
2. The other instance where you're using "als" may be a bit confusing now, as it means "as". "I want to work as an engineer" = "Ich will als Ingenieur arbeiten"
I hope this helps and doesn't confuseyou even more. Maybe you should just learn it as vocabulary instead of grammar: "than = als", "as [big,...] as = wie", "as [a job,...] = als"