Your question is a bit vague. Most DOCTOR WHO stories take place on Earth, and they certainly don't go into much worldbuilding detail about other planets.

The only ones that are really prominent are:

SKARO - homeworld of the Daleks. A formerly Earth-like world devastated in nuclear war. The planet and the entire star system are inadvertantly blown up by the Daleks themselves using a booby-trapped device (booby-trapped by the Doctor, naturally).

GALLIFREY - the Doctor's homeworld. A large planet (significantly bigger than Earth, though not a gas giant) mostly made up of wasteland and desert, aside from a few major cities populated by the Time Lords.

MONDAS - Earth's former twin planet, blasted out of orbit millions of years ago. Its people eventually became the Cybermen.

TELOS - The Cybermen's second homeworld, adopted after Mondas is destroyed. A frigid ice world. The natives, the Cryons, eventually overthrow the Cybermen, reducing them to a nomadic species constantly on the run through space.

PELADON - a medieval, feudal planet contacted by far-future Earth and eventually brought up to technological parity. The planet is divided between factions feuding over whether they should accept outside help or not.