(someone) is supposed to (do something)

Say that someone "is supposed to" do something if:

• there's a rule about it
  

  I think we're supposed to shower before going in the pool.

• there's a custom that says something about it
  

  You're supposed to take your shoes off when you go into someone's house in Japan.

• you have already agreed to do it
  

  I'm supposed to pick Janelle up from school this afternoon. 

Note that "supposed to" can also be used in other situations, like when you're reporting information that you heard from other people.

re-(do something)

"Re-" is a prefix that means to do something again. You can use this prefix to make a lot of English words like:

resend

rearrange

rethink

remake

rewrite

apply sunscreen

To "apply" sunscreen means to put it on someone (yourself or someone else).

The word "apply" sounds technical, so you would use it in situations like when you're giving someone instructions. The sunscreen bottle will probably use the word "apply" in the instructions, for example.

In more casual speech, you can use "put on" instead of "apply":

Don't forget to put on sunscreen!

You can also "apply" things other than makeup:

• Apply makeup.
• Apply a cream or ointment to a cut on your skin.
• Apply glue to something that you're trying to stick together.
• Apply a wood-sealing liquid to the wood on your porch.

every few / every couple of (minutes/hours/days/etc.)

Use this expression to talk about something that happens again and again after a certain length of time. For example:

I try to call them every few days, just to make sure everyone's OK.

This sentnence means that the speaker calls again and again, with 3-20 days of not calling in between each time.