What do I paint when I first begin to learn oil painting?

This is the question many people beginning to learn how to paint with oil paints ask. For an answer I recommend you try all the different subject types to get some painting experience with all of them and then you can decide what subject you like the best. The subjects you can choose from are:
Landscape
Seascape
Cityscape
Floral
Still Life
Portrait
*Human (face or whole body)
*Animal
Abstract
Fantasy

There are many more but these will get you started. For beginners I recommend doing a few still life paintings as you can control the lighting and subjects.
Try as many of the different types of painting subjects as you can so you can decide what you enjoy painting the most. Then do your favourite subject.
With my own experience I began doing landscape painting and some still life and floral paintings. I have gradually gone on to doing portraiture. I still love to paint landscapes but would like to get better at doing portraits.
If you find you are trying a new type of subject matter and learn you don't enjoy that particular type of painting then you don't have to keep on doing that subject. Stop and try something else new you haven't done before.
The main thing is you should enjoy the painting process and you will be getting valuable experience too.