Ok, now I've got it, don't worry.
You have a chain with 4 C-atoms: one of these atoms is the one bonded to the OH group and double-bonded
to O. This is called carboxylic group and has the highest priority: that is why it is your 1.
Then you have 3 C: they are 2, 3 and 4. The second (the closest to COOH) is bond to an H-atom and to a methylic group (-CH3).