"I used to ... " is somewhat similar to the imperfeito in Portuguese. It means that you previously did something continuously. However, in English, "used to" also implies that you presently don't do this action: "I used to walk to work, but now I drive my car (so, I don't walk to work anymore)." "I am used to ..." means that you are in the habit of doing something. You are accustomed to doing something: "I was used to eating eggs for breakfast, but in Italy I ate only yogurt." "I'm used to going to bed early, but last night I went to bed at midnight." Be careful not to confuse the special cases above with the normal use of the verb "to use" (see below). Summary: "I used to drive a car." = In the past, I often drove a car, but I don't anymore. "I am used to driving a car" = I usually drive a car/I am accustomed to driving a car. "Yesterday, I used a car" = Yesterday, I drove a car (simple past tense like pretérito). I hope that helps! If you need any more help, I'd be happy to offer more examples.

The others have answered the question perfectly; however, don't forget that "I used to..." is followed by the simple present form of the verb, and "I am used to..." is followed by the gerund (-ing) form of the verb. The form of the verb tells the listener or reader which meaning you are using of this phrasal verb, so it is important! See the examples from the others above.

"I used to say..." is for things you said in the past, but don't say now. "I used to say that strawberries tasted awful... but now I love them." "I am used to saying..." means you are accustomed to saying that. "I'm used to saying my name in an Irish accent."

Examples: I used to say that I would always wear black. Now I have changed my mind. I am used to saying "You're welcome" everytime I get thanked for an answer.