Im not very knowledgeable about the human body so all help is needed.

I do have one kid and it took us about 8 months to conceive. Last november i was pregnant, then had a miscarriage. Getting pregnant that second time took about 2 and half years. We are ready for another child. :) Are ovulation tests a waste of money? Should i try at least one? When should i try it? I know everybody is different, but about how long does ovulation last? How do i know when im ovulating? Any other information is welcomed! Thanks!!