This should help you when you are using levers or any other constant redstone input.
For buttons it would be a bit more complicated unless the buttons are that close that you could have them all pressed at the same time.
If you still have troubles to rebuild what azarjeazar777 explained I would recommend you to look in the minecraft wiki or youtube for an "AND Gate". Thats what you basicly need to realise what you are looking for.
you can hook up the buttins to a R-S nor latch....