Ok so I just started a test based game with a script and theres a whole bunch of glitches, the one i need to fix mostly is that people can send more ingame money than they have by typing + infront of the number and - after ....A friend told me to validate the database or something but i dont understand how to do that and all of the guides when i google it are extremely advanced. And I dont understand php so please make this a noob guide 
thank you in advance
thank you in advance