Conditional Clauses

Take a look at these examples:

If you heat ice, it melts. (= Ako zagreješ led, on se topi.)

If you don't heat ice, it doesn't melt. (= Ako ne zagreješ led, on se ne topi.)

If it rains, I will stay at home. (= Ako pada kiša, ostaću kod kuće.)

If it doesn't rain, I will not/won't stay at home. (= Ako ne pada kiša, neću ostati kod kuće.)

If I had money, I would sail round the world. (= Kad bih imao/la novca, plovio/la bih oko sveta.)

As you can see, all these examples start with IF and talk about a situation/condition and its result. When this is the case, the conditional clause is separated from the main clause with a comma. 

The situation described in the above sentences is always true (Type Zero Conditional), sometimes possible (Type 1 Conditional) or unreal (Type 2 Conditional). That is why we use the present simple tense in the Zero Conditional, present simple and future with WILL in Type 1, and past simple and WOULD with infinitive in Type 2.