The difference between its and it's

Some students still get confused when it comes to using 'its' and 'it's'. Hence the following sentences often appear in essays submitted by them for correction by their teachers:
1 The cat licks it's body every day. (The students think that it's body means the cat's body)
2 One of it's tyres is flat. (The students believe that it's tyres is the same as the bicycle's tyres)

The above two sentences should have been:
1 The cat licks its body every day.
2 One of its tyres is flat.

In reality, "it's" is the contraction for "it is".

You can make sentences such as the following.
1 It's raining now.
2 It's easy to do this job.