Chemistry question

I understand the calculation part but don't get how to actually form the equation with the information like usually we are given the reactants and products and form the equations but I'm struggling to understand how the equation is done

They’ve told you that you have FeSO4.7H2O and K2Cr2O7 (acidified) as your reactants.
You need to learn that whenever something reduces K2Cr2O7, it will generally form Cr^3+ and so the chromium changes oxidation state from +6 to +3.
Iron only has a few common oxidation states. Anything other than 0, +2 or +3 is uncommon. Since the iron is in the +2 oxidation state and must be oxidised rather than reduced, it must be go from +2 to +3.
The easiest way to deduce overall equations for redox reactions like this is to use the change in oxidation states method, but you can construct and combine half-equations if you prefer.
Since the important element in the oxidising agent (Cr in K2Cr2O7) changes its oxidation state by 3 (+6 -> +3), the number you put in front of the reducing agent must be 3 x 2 = 6 (multiplied by 2, since there are two chromiums per formula unit of K2Cr2O7).
Since the important element in the reducing agent (Fe in FeSO4.7H2O) changes its oxidation state by 1 (+2 -> +3), the number you put in front of the oxidising agent must be 1 x 1 = 1 (multiplied by 1, since there is only one iron per formula unit of FeSO4.7H2O).
So we have
6FeSO4.7H2O + K2Cr2O7 + (acid) —> (products)
We could finish off the equation and add more detail, but we really don’t need to - the most important feature of the equation in this case is just the ratio in which the reactants react, which we have - it’s 6 : 1.