Usually, Used to, Be/Get Used to

 Let's try to see the main differences among these three forms, according to the tense and the meaning, and to the following form. 

The first difference is the TENSE they are used and it's meaning:

• USUALLY is for any tense but it's very likely to see it with present simple or habitual present and it's related to how frequent you do an action:
• She usually goes to work on foot
• USED TO is only past and it has the meaning of having done something in the past but you don't do it anymore, that is, habits or actions you stopped doing them.
• She used to go to work on foot but now she goes by car
• BE/GET USED TO: it's used for any tense as the form "used" is taken as an adjective, not a verb, so the tense is shown in the verbs "be" or "get".
• She's not used to going to work on foot anymore as she goes by car

The other remarkable difference is the form following the expression, especially between "used to" and "be/get used to":

• USUALLY+ present simple or other tenses: I usually had fish during my last holidays (pay attention it doesn't mean I don't do it now, just it was something habitual in that time)
• USED TO + infinitive:  I didn't use to have fish when I was a child (this fact happened in the past but not now)
• BE/GET USED TO+-ing form: I got used to having fish when I was in my twenties (notice that TO is a preposition here and not part of the infinitive, so it's followed by -ing form)

There is a little difference between using BE or GET in this last form: "to be used to" means you're familiar with that action while "to get used to" means you're in the process; if you want to practise with this, do this exercise

Just to finish with this difficult point, there is a blog with an entry in Spanish which works with more differences among these forms. If you feel confident enough to fgo a bit further with this matter, visit this link.

You should practise with written exercises but first have a look to this explanation in Test English and then do these exercises:    exercise 1  (there are 2 more exercises)    exercise 2    exercise 3

Once you've understood this, practise with these questions but do it as oral practice:

• What did you use to do as a child in your free time?
• What do you usually do to relax?
• What won't you get used to doing as an elderly person?