I am newbie in sims 2....how to do that shift click thing to make the needs stay same forever?

You could do it like the other person said, but you said you wanted them to stay the same and not have to drag them up when they get low. In order to do that you have to do Crtl+shift+c, and then type in boolProp TestingCheatsEnabled true after doing that hold the shift button and then click on the mailbox and you should see a thing that says "Make needs static" or "Make motives static". Click that, and now your sims needs won't decrease, they'll just stay in the green the whole time. Hope I helped!