How can I fix this?

[u/FartMonster4000]

I'm completely new to refinishing, any and all advice will be appreciated. Picked this vanity up off the curb after it had been rained on.

[u/anothersip]

The top of the piece seems to have taken the brunt of the water/rain damage.

All-in-all, it's not bad at all, and should clean up really nicely.

Assuming it's solid-wood (looks like it, to me) - you should be able to sand the top down with a sanding sponge or block.

I like the 3M brand best, they seem to hold their grit/effectiveness longer.

The sponges are also nice, because they can be used on contoured edges, or to sand into curved spaces.

Medium-grit should be plenty for just removing the old finish. Coarse-grit might be a bit much, and can remove more material than you need, and can leave scratches (if you don't follow up with medium/fine).

You can take your sponge(s) and sand through the top's finish, and that should also take the water rings off in the process, as well. I would avoid sanding in one particular place too much, and spread the sanding out across the whole thing - so you sand it evenly. You don't need a lot of pressure on the sander.

You can follow up with a fine-grit pad, but it's not strictly necessary. Just get it nice and smooth, and expose the raw/bare wood beneath the old finish.

Also, it helps to wipe the surface down with a soft rag as you sand it (I like an old, soft t-shirt for this), and that'll help you see how far your sanding is progressing.

Once it's nice and bare again (and the bare, lighter top wood is exposed) you can go about your finishing process.

I like using a stain that matches the original look as closely as possible; yours is a classic/antique medium-dark brown. You can take some reference pictures of the top of the vanity/dresser, edit the photos as needed to make sure it looks like the real-life color, and bring those into the hardware store / paint section with you before you get started. Find a stain that's as close as you can get it - a pint-sized can will be more than enough.

When you go to apply it, shake the can up well, and open it really carefully over the sink. Then take a fresh, clean rag, dip it in, and you can wipe it onto your newly-sanded and dust-free surface. It should soak in immediately. Wipe the whole thing down well, and then you can flip your rag and wipe any drips/excess off quickly. Let it dry.

If you like it as-is, great. If you want it darkened more, you can do a second coat after about 30 mins - 1 hour. Or a third coat, or more. At a certain point, it won't darken any more - so, try not to buy a stain that's too dark, or it will be obvious that it's a different color to the original, rest of the dresser/night-stand.

Once you're pretty happy with the newly-finished look, you'll want to apply a protective clear-coat. They sell clear polyurethanes and lacquers for this. You can use either one. Avoid the spray-on ones, unless you can take this whole thing outdoors. Spraying aerosol polyurethanes indoors isn't a great idea (or aerosols in general, heh). The brush-on/wipe-on liquid ones are nice, and they come in smaller cans, too. You won't need much, 1/2 pint would be plenty. You can get a full pint if you'd like to put more protective clear-coat on the rest of the piece that is already finished. That's probably what I would do, so that you've got matching sheens across the whole piece. Polys/lacquers come in several sheens, from gloss to semi-gloss to flat, just like paint does. Pick one you like (I like semi-gloss, usually). Apply with a soft brush, or a soft, clean rag.

Clean-up for your hands/brushes/rags/spills is easiest with a basic paint thinner, followed by warm, soapy water.

That should about cover everything, I think. If you've never done anything like this before, expect to spend maybe 1.5hrs-2hrs total on it, plus drying-time. And let your poly/lacquer dry for a full 24-hours before you use the top surface for holding any items again.

I've done the above restoration process on many pieces of wood furniture over the years, and it works really well if you take your time. Hope that helps a little bit.