It's possible someone bought an unfinished table.

Make sure it's clean ... Then sand it lightly, stain it if you want to, then apply a coat of any coating meant for furniture. Follow the directions on the cans.

Put several coats on the top because that's where the stains will land.

Sand with 150 grit paper, hand(---follow the grain) or random orbit sander.

I recommend varnish for tables. Not polyurethane varnish, just plain old varnish. Because it is durable, resists scratching/staining and can be fairly easily repaired.

Polyurethane cannot be spot repaired and chips.

I buy varnish at Sherwin Williams, but most brand name paint stores have comparable products. The stuff in a home improvement store can easily be way over the Use By date and seems to me to be an inferior product.

Sherwin-WIlliams Fast Dry Varnish
Pratt & Lambert #38
Waterlox Original
Cabot 8000 (nee McCloskey's Heirloom)

all non-poly varnishes

Behlen's Rock Hard used to be, but I have heard they've reformulated .