For Vada.. Wash dal several times and soak in lot of water for at least 4 to 5 hrs.
Drain the water completely and transfer the dal to a mixer grinder jar. If you have a wet grinder, you can use it.
Sprinkle very little water. Next add salt and start grinding.

Transfer in the bowl and beat it for some time so that air fils in the batter.

Heat oilin a kadai, add a small batter to see if oil is hot.

Take a small portion of batter in your hands wet your hand and give the shape of the vadas. Slowly put in oil and serve hot with sambhar.

For Idli.. Wash the urad dal, soak the urad dal and idli rava in separate bowls. If you are using flattened rice, soak it also in another bowl. Let it soak for at least 1 hour.
Grind the soaked urad dal and poha using a wet grinder or mixie to a smooth batter. Remove it into a big bowl.

Squeeze out the excess water from the soaked idli rava between the palms and mix with the ground urad dal batter.
Mix required salt, cover with a lid and keep it in a warm place to ferment for about 10-12 hours.

After fermentation, the batter would have doubled in volume.
Grease the idli plates, pour a ladle full of batter to fill three fourth of the moulds. Steam it for about 7-10 minutes.. Serve with hot sambhar