You can Add your period in Ela and basis the cycle and the initial information you provided like cycle length, period length etc, it will predict the fertile window. You can see the best 5 days highlighted in blue. You have the highest chances to conceive during these days and should have intercourse atleast alternate days during this time.
@Anita: You can add your past period dates on the Ela App by selecting the circle on the home button. Based on your past period dates, Ela will predict your next cycle.