I have some water marks on the ceiling of my home. How to fix?

First I would find the source of the water that left the marks and fix that first. Then clean and repaint the ceiling.

that covers stains and it should be available at you DIY I think it is called

"Stain Block"

1. seal the stain... use flat paint only. 2. I used a sponge to paint flat white over the stain. 3. feather paint out at edges. If the ceiling was painted some time ago you might want to have a beige water paint on hand to make your new area stick out less,

sometimes it's condensate from your water pipes or air conditioner. strange but true, sometimes water travels along electric wires that come from outside. use Kilz for the stain. and repaint if you have to.

Suggest you check the attic for mold, which might be toxic (sorry).

Check to see if you have a leak in your attic, then check the roof. If you have water marks, the water is coming from somewhere. You don't say what floor the leak is on. After you find this out, have it fixed, then paint it. If is slightly cracked, you'll you'll need to repair the ceiling. Good Luck!

Definitely try and find the sneaky water, or you'll keep doing this! A stain blocker is right, as @Johnavallance82 said. In the States, you can use several types: Shellac, or a Shellac based product, which I am not sure is carried in California, where you are.

There are also great water based/low VOC and probably to your local code products made by good brands like BIN, KILZ and Zinsser. Use a stain blocking primer, before you paint, and if your colour is deep, have the store tint the primer a bit, so it won't be so hard to cover.

I have decades of experience and you can get primer and paint combos, but they are NOT the same quality. If it's an area you don't care about that much; go for it. But the prep work is 90% of the job and if it's poorly done, like not fixing the leak, it will come back to haunt you! Also, people love the brands that the Big Box stores carry. For coverage? I don't. Spend a bit more on the paint you would get from a dedicated paint store. Trust me, you can tell the difference:

The pigments carry further and reflect light in ways that are so much better. And the surfaces are hardier for wiping down, which has to happen, once in a while. (Particularly if you have people who touch walls in your house!)

Also, if you have an older house, your plaster that got wet will need to be treated with Muriatic Acid, as the water will have activated the microbes in it. If you see puffy looking dust "blossoming" from the ceiling, that's exactly what it is. The area will need to be scraped back as far as the loose plaster can be, then you CAREFULLY pour I believe a 1:10 ration of MA into H20. Soak the area with a chip/disposable brush, using eye protection, gloves, face mask, etc. When that is dry, then prime and paint. If it's sheetrock, you can just cut away the wet 'rock and sister in some new.

where the water ended up may have started several yards away. if you have an attic check for water staining under the roof , if your water pipes are in the attic is condensation a problem? house no.1 was on a slab foundation. wet spot on bedroom ceiling yup....water line.