I have trouble understanding the words on, in and at.
I mean, how do I use them. Like I've heard people saying:

-I'm in my way, but I have also heard, I'm on my way?
-I'm at the mall, and then I'm in the mall?
-It's in the home department, why is it in and not on?
-At her birthday party?
-He's in the yellow shirt?

I really need help, and please don't tell me to read books because I've read quite a lot of them; but I'm still having confusion. Please, if you know about a trick to understand them better, let me know. I will really, really appreciate it!

Thank you!

Question

I have trouble understanding the words on, in and at.
I mean, how do I use them. Like I've heard people saying:

-I'm in my way, but I have also heard, I'm on my way?
-I'm at the mall, and then I'm in the mall?
-It's in the home department, why is it in and not on?
-At her birthday party?
-He's in the yellow shirt?

I really need help, and please don't tell me to read books because I've read quite a lot of them; but I'm still having confusion. Please, if you know about a trick to understand them better, let me know. I will really, really appreciate it!

Thank you!

Answer

- in : wearing something
'He's in the yellow shirt.'
'Dressed in their best clothes'
'She was all in balck'

Answer

- At her birthday party: Correct
We say that somebody is AT an event:
at a party / at a conference / at a concert / at a footaball match / at the wedding...

Answer

On the home department: incorrect
We use 'in' with buildings: In the home department

Answer

- 'I'm at the mall': is correct.
We ususally say 'at' when we say where an event takes place:
'I had dinner at the hotel.'

- 'in the mall': is correct
We use 'in' when we are thinking about the building itself:
'The store has a prime position in the mall.'
'All the rooms in the hotel have air conditioning.'
So we can often use 'in' or 'at' with buildings.

Answer

- In my way: is correct. 
= stopping somebody from moving or doing something
'You’ll have to move—you’re in my way.'

'In my own way' is another expression meaning in a manner that is typical of me:
'I like to live my life in my own way.'

- On the way: is correct (= during the journey)
'We stopped at a small village On the way to London.'
'I dropped my keys in my way out.'