How do I graph f(x)=x^4-2x^3-5x^2+6?

To make sense for a graph you change it to:

y = x^4 - 2x^3 - 5x^2 + 6 Also adding spaces to improve readability.

I don't know what you are talking about re "grouping" or "x intercept". The plot looks like this:
www.wolframalpha.com/input/?i=plot+y+%3D+x%5E4+-+2x%5E3+-+5x%5E2+%2B+6

To sketch the plot you would differentiate to get:

4x^3 - 6x^2 - 10x = 0

x(4x^2 - 6x - 10) = 0

x(x + 1)(x - 5/2) = 0

x = -1, 0, 5/2 These are the inflection points where the slope = 0.