LIKE versus AS

The main differences between LIKE and AS are:

• about meaning: She works AS a doctor (she's a doctor) while she works like a doctor (she isn't a doctor but similar)
• about grammar: LIKE goes with a noun or pronoun; 

For a good explanaition go here

Used to

Used to is a verbal form to speak about something you did in the past but you don't do it any longer. Here you have some links to help you:

• an explanation with exercises at the end; click here
• a shorter version; click this
• another one but they introduce would with this meanining; click here
• last exercise

The most important thing is to use it while speaking because it's quite easy when you use it in texts.