Click on the following box and put the cursor in it. The bottom image is just for reference of English key combination and its relevant Tamil letter. You cannot click on the image. Now suppose you want to type "தமில", they you have to type "tamila". Here small letter and capital makes difference so make sure that "Caps Lock" key is off. when you type "t" it will type half letter "த்" and when you type "a", it will complete the letter "த". For complete typing tips, please visit the page Indian Language Typing Tips.