Should Terms and conditions for shown before the user click the sign up button or after. (after with means of the same page below the sign button)
From a legal standpoint, the Ts & Cs should be available to the user before they fully commit to purchase the product or service.
In other words, you have to give them a chance to understand what they're buying into before they actually buy into it.
As pointed out in the comments, users tend to ignore these and just assume that they're getting what they expect. This is mostly because they are so long winded and worded in a careful way to make them difficult to understand.
Making this the very last step before legal purchase leverages loss aversion. The user has put some effort into making this purchase and they're now only one click away. Whereas, placing the Ts & Cs earlier in the process reduces the amount of effort the user has invested up to that point so the loss aversion is reduced.
Basically, put it as late in the process as you can but make sure the user can still opt out if they don't like the terms.
If you mean the sign-up button on a sign-up form, then you should absolutely provide some method of letting the user see your Terms and Conditions before they sign up, not afterwards when it is too late.
Many websites and programs use a "I accept the Terms and Conditions" tick box that prevents the user from signing up before they accept the terms and click the tick box. A link to the T&Cs is provided nearby, either below the tick box as its own link or as part of the tick box's description text.
This method still informs the user that T&Cs do exist for what they are signing up for, but is non-intrusive for those who have already read these terms before (if they've used your service before or viewed the T&Cs before they started signing up) or for those who don't bother reading them (which is a reason why you should provide both a friendly, easy to understand version for the less patient as well as a regular verbose version for those who do care. Google does this quite well in my opinion). It doesn't force people to read your T&Cs too (forcing people to read them doesn't improve UX), and to be honest, when I'm hit with a large wall of terms and conditions, I just want to scroll through the whole thing to make it end or just outright ignore it.