Is this bulb good for flowering plants?

Not really. At 5000 K it is a cool white light with limited red, which suits leaves and vegetative growth better than flowering or fruiting. Plants grown for blooms or fruit do better under warmer or full-spectrum grow lights.

How many bulbs do I need for a shelf of houseplants?

Plan on one bulb per small cluster of plants directly beneath it. At 12 W the useful light falls off quickly with distance, so a long shelf needs several bulbs spaced along it.

Does it fit a normal lamp socket?

It is a BR20 bulb, a standard-shaped reflector bulb that fits common medium screw sockets. Check that your fixture's wattage rating covers a 12 W LED.

Can I use it in an ordinary room light?

Yes. The 5000 K white light reads as a bright cool white, so it works in a normal fixture without the purple glow of blurple grow lamps.

How long will it last?

The bulb is rated for 25,000 hours, roughly several years of regular daily use. Cheap LEDs often dim before they fail, so expect output to drop over time.