1. In general, we are going to use the simple future tense in Spanish to say what we think it will happen, but also to express an intention or a probability, to make a promise, also to talk about events that will probably happen depending on conditions:
Creo que Fernando y Marta se casarán el año que viene (I think Fernando and Martha will get married next year).
Te prometo que iremos de vacaciones pronto (I promise to you that we will go on holidays soon).
Si terminas de trabajar pronto podremos ir al cine (If you finish working son we will go to the cinema).
2. You can use the simple future tense in Spanish to make a guess about the present or to make a hypothetical question.
Gustavo tendrá 40 años, su hermana tiene 42 y es mayor (Gustavo will be 30 years old, his sister is 42 and she is a bit older).
¿Dónde estará Mercedes ahora? (Where Mercedes will be now?)
3. In English, you sometimes use will with the meaning of being willing to rather than simply to express the future. In Spanish you don’t use the future tense to say this; you use the verb querer (want) instead:
¿Me quieres esperar un momento? (Will you wait for me a moment, please?).
Finally, remember that there is another future tense called FUTURO IMPERFECTO O COMPUESTO.