Verb tenses

Hello friends, I'm learning a lot of Hindi verbs and I'm really confused with all the tenses, gender and basic sentence structures.
Please help me and correct me :D

I learn Hindi
Mein Hindi seekhtee hoon

Are you eating an apple?
Kya tum seb khaa rahe ho?

(tum, aap and tu have same meaning which is "You", however aap is used for elders or to give respect to people, tum is again for respect but people of same age(designation) or lower age and (designation), but tu is more of a informal which is used in between buddies or people who are alot younger to you.... here is how you should use it with Aap and tum rahe ho and with tu raha hai)

I don't understand
Mein samaghtee nahin hoon (Mujhey samajh nahi aata should be more appropriate)

I speak English and Chinese very well
Mein angrezi aur cheenee achha bolti hoon

This is Pooja's dog.
Yeh Pooja ka kuta hai. (we use ka for male and Kee for females)

They are beautiful girls.
Ve sundar larkiyaan hain.

We are not drinking water.
Ham pani nahin pee rahe hain.

She is my friend.
Voh mera dost hai.(friend is dost & friendship is dosti)

I learn Hindi
Mein Hindi seekhtee hoon

Are you eating an apple?
Kya tum seb khaa raha ho?
Kya aap seb khaa rahe ho? (for showing respect, you can use aap. Accordingly, the verb changes to rahe ho)

I don't understand
Mein samaghtee nahin hoon

Main samajhee nahi

I speak English and Chinese very well
Mein angrezi aur cheenee achha bolta bolti hoon

This is Pooja's dog.
Yeh Pooja kee ka kuta kutta hai.

They are beautiful girls.
Ve sundar larkiyaan hain.

We are not drinking water.
Ham pani nahin pee rahe hain.

She is my friend.
Voh mera dosti dost hai.