You might want to provide more details, e.g. soil, how long its been in that pot, how often you water, how squishy the leaves are..etc but based on this pic alone:

The bottom leaves look like they are rotting (squishy? smell kinda funky?), the soil looks too wet for succulents. (research gritty mix)

Take out, remove soil, easiest when soil is dry, since this looks like an emergency just do the best you can to examine how much rot there is.

If not a lot of rot, behead with clean knife above the rot and wait for cut to callous over, don't leave under direct sunlight (2-3 days depending on how dry your place is).

Since your bottom leaves are already affected, the rot may have reached the main stem. You have to check yourself, in that case may be more successful to pull off healthy leaves and lay those on top of soil and wait for pups to come out.

I bought it a week ago and since then i kept it in its original plastic pot,watered it once and kept it indoors. Leaves are brown near the steam.

Usually with new succulents, you should check its root by taking it out of the pot and removing the soil. If the soil isn't good, replace or amend it so that it is gritty for succulents.

How much light does it get? Succulent plants need a lot of sunlight, this looks like an echeveria and it needs a lot of light. (When adjusting it to more light, do it in stages or you may risk sunburning it depending on where you live).

When you say brown, is it brown dry or brown squishy?

Check the roots/main stem for rot to decide what next actions to take.