Aaj chutti hai!

Namaste! Aaj se meri garmiyon ki chuttiyan ki shuru ho rahi hai. Kitnu main bahut thaki hoon, kyonki school ke ant se pehle main ek bari  (what do you mean to say by "ek bari" to be precise?) meri pareeksha thi! Aur ab mere paas zyada chuttiyan  chhuttiyon ki homework hain, to main thodi vyast hogi rahungi. Yehi meri zindagi hai! Lekin kabhi kabhi vyast rakhne  rahane mein accha lagta hai; mujhe school bahut pasand hai. Main  Mujhe school ko prernadayak aur dilchasp lagta  lagati hai. Aur ye chuttiyan Christmas ki hain! Mujhe Yishu ke karan Christmas bahut pasand hai.
Merry Christmas, aur naya saal mubarak ho!

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Bahut Badhiya!! :) So well written, I am Impressed ! 

Aaj chutti hai!

Namaste! Aaj se meri garmiyon ki chuttiyan ki shuru ho rahi hain. Kitnu Kintu main bahut thaki hoon, kyonki school ke ant se pehle main ek bari   meri ek badi pareeksha (I suppose you mean to say - a big exam or a difficult exam) thi! Aur ab mere paas zyada chuttiyan  chhuttiyon ki  ka homework hai, to main thodi vyast hogi rahungi. Yehi meri zindagi hai! Lekin kabhi kabhi vyast rakhne  rahane mein accha lagta hai; mujhe school bahut pasand hai. Main  Mujhe school ko prernadayak aur dilchasp lagta  hai. Aur ye chuttiyan Christmas ki hain! Mujhe Yishu ke karan Christmas bahut pasand hai. 
Merry Christmas, aur naya saal mubarak ho!

Larissa apne bahut achcha likha hai.

Agar aap Hindi alphabet sikhna chahtee ho to main aapki madad kar sakta hoon.

aaj se chhuttiyan hai!

namaste! aaj se meri garmi ki chhuttiyon ka shuruaat hai. lekin main bahut thaki huyi hoon, kyonki school ke ant se pehle meri ek baRi pareeksha thi! aur ab mere paas kaafi saara chhuttiyon ka homework hai, isliye main thoRi vyast rahoongi. yehi meri zindagi hai! lekin kabhi kabhi vyast rahna accha lagta hai; mujhe school bahut pasand hai. mujhe school prernadayak aur dilchasp lagti hai. aur ye chhuttiyan christmas ki hain! mujhe yishu ke karan christmas bahut pasand hai.
Merry Christmas, aur naya saal mubarak ho!

Excellent job, just minor structural corrections :)

Note that the capital R is used to indicate the retroflex r (ड़) of Hindi, the capital T is used to indicate the hard t sound (ट) and the capital D for the hard D sound (ड). That is why no other letters are capitalized, including sentence beginning and proper names when using the simple Roman alphabet. If you use IAST, then that has a different set of diacritics to accurately represent Devanagari script.