how to find interaction terms in regression modeling


Less is more. Stay pure. Stay poor.
Typically there should be some rationale behind the exploration of interaction terms, otherwise you are just mining for significance and it may present itself randomly without logical or real cause.

Exploring all terms can be achieved different ways with different software. In SAS you can seperate terms with| and add @2 at the end of the model statement for 2-way interactions and @n, n any integer, for higher order interactions.
Well, an interaction is simply a multiplication of two (or more) variables. So, if your model is y=a+bx1+bx2+u, then the model with interaction would be y=a+b1x1+b2x2+b3x1x2+u.

Keep in mind that adding interactions (could) increases the multicollinearity. A good reference book, from my point of view is:
Aiken, L. S., & West, S. G. (1991). Multiple regression: Testing and interpreting interactions. Sage.