Participating in activities that involve the development of CV endurance like aerobic exercises should last between 15 to 30 minutes of light to moderate intensity and doing this 3 to 5 times a week will help increased aerobic capacity in about 8 to 12 weeks.
Moreover, it is good to start from simple activities such as walking, stair climbing, jogging and running then advance to cycling, swimming, rowing and hiking as your body increases stamina and endurance eventually. Also, it is important to ask for help to knowledgeable fitness professional the number and length of training and rest intervals.