Is this your first tank?
The tank needs to cycle before you can just throw in fish. Cycles can take anywhere from 2 days to 4 weeks.
It doesn't appear that you have a heater and a thermometer in the tank, which oscars and most other fish will need.
Do you have a test kit either? You'll need that to test ph, ammonia, nitrite, and nitrate which must be at the correct levels that are safe for your fish.
First though, to get the cycle started you should ask someone with an established tank to borrow a couple of their tank ornaments or a bag of their tank gravel which has beneficial bacteria living on it. Then put that in your tank to make bacteria start growing in your tank. After getting a test kit, you'll need to test the water and match the correct levels (the test kit should come with a chart) every couple of days. Once all of the levels are correct you can start adding fish.