The conjunction se corresponds to if and is used in conditonal clauses, see 13. o condicional. There are three types of conditional clauses. (Actually there are more, but these three types are mentioned in grammar books all over the world for any language.)
type I condition probable
Se voc� o quer, lhe darei.*
If you want I will give it to you.
type II condition possible
Se eu tivesse dinheiro, eu o compraria.
If I had money, I would buy it.
type III condition impossible
Se ele me tivesse pedido, eu teria dado.
If he had asked me, I would have give it to him.
* Actually there should be an o there, a personal pronoun refering the thing he gives him. However lho is not very common in Brasilian Portuguese and is therefore often left out. If one ones to mention it, it would be more common in Brasilian Portuguese to do that with isso: Se você o quer, lhe darei isso.
The conjunction se doesn't surprise us. What surprises us is the fact in the conditional part of the sentence, the part that describes the condition, the futuro do conjuntivo is used. That doesn't comply really whith what has been said about the futuro do conjuntivo, see 12.1.5. We have said that the futuro do conjuntivo is used when there is no uncertainty concerning the question whether the action / event is going to happen, but it is unclear when it will happen. This is not true in conditional clauses. In conditional clauses of type I, where the futuro do conjuntivo is used, it is unclear whether the condition will be fulfilled or not. However we don't have either a subjective evaluation, we have a logical relationship. If A is true, B will be true as well. The other roman languages use the indicative in this context. In theory we have the choice between the presente do conjuntivo (this option is incorrect in any roman language), the presente do indicativo (this is option used in other roman languages) and the futuro do conjuntivo (this is how it works in Portuguese). If we take into account the Portuguese logic, that differs from other roman languages in this case, the futuro do conjuntivo is the most plausible verb form.
We repeat. In the case of regular verbs the 1st and 3rd person singular the futuro do conjuntivo doesn't distinguish itself in the form the infinnitivo pessoal or the infinitivo. One could therefore get the idea that there is an infinitivo (pessoal) in the if clause, what is not the case. The infinitivo (pessoal) is not possible in a subordinate clause because in a subordinate clause we need a finite verb and not a verbal noun. Those who have forgotten this can go back to 18.1.5.
If you want I will give it to you. 
