A Jaati is a pattern that gives us the basic feel of a Thalam. Read the article Tala System to get a hang of how it works. What you need to understand as a beginner of Bharatanatyam is that there are five Jaatis. Every jaati is denoted by a set of syllables. They are:
The Tishra, Chatushra, Khanda, Mishra and Sankeerna.
They are nothing but rhythmic patterns followed in Indian classical music. In Jaati Adavu we will learn feet movements on these patterns. The focus is on the leg movements. Hand movements keep varying as per need. Following are the videos for the jaati Adavu