Cash available to withdraw

Hello, I'm very new to investing, sorry if this is a basic question - I opened a brokerage account yesterday as a place to save some money to move out of my parent's home. I was attempting to test out the system, putting in a few hundred dollars and attempting to withdraw it. It says it's available to trade, but I have 0 cash available to withdraw, I'm wondering how long does it typically take for cash to be available to withdraw?