A broker facilities trading between market participants, allowing you to buy stocks from sellers and sell stock to buyers (there is a buyer and seller for every transaction). As a trader you want a broker that is:
Low cost (low commissions and fees)
Reliable (can trade when you want, with minimal system outages)
Honest (won't steal your money, or engage in risky behaviors with it)
Gives you tools for research (least important, since there are loads of free tools available online)
If you want to day trade, there are a few more things you may want in a broker.
The broker should execute orders instantly. No intervention on their part. Even a one-second delay is too much.
"Trade from chart" capabilities, and/or ability to rapidly place, adjust and cancel orders.
There are loads of brokers, some of which are better for investors and some which are better for day traders or swing traders. Picking a broker is the biggest trade of all; all your capital is given to this company. Spend time researching the above factors before choosing a broker.
Each broker offers a trading platform. This is the technology that allows you to view stock quotes, see charts, do research and most importantly place orders. Test out various platforms by opening demo accounts with various brokers.
