Few days back, i got a pug puppy who is just 45 days old (1 and half month). I am bit concern because he is too young. Please advice me the basic things from which i can start to train my puppy, nutritions, cleaniness and understand him in a better way. I will be highly obliged if you can suggest me the best way.
Is it your first dog? Then the basic steps are as follows:

1) Right nutrition
Any dog food you choose should be intended specifically for puppies. Canned food is OK but dry food is cheaper and better for teeth. Avoid generic foods and those at too low prices. It is better to choose well-known brands (even though there've been many talks about their doubtful ingredients, you're less likely to buy something of a bad quality). Make sure that the food is intended for small dogs.
Puppies should be fed around 3 times a day. But basically, just watch how much he eats and reduce the frequency if he isn't hungry. Let him eat as much as he wants for around 15 minutes, and then take the dish away: pugs gain weight very easily so do not provoke it by leaving the food bowl (but a bowl with fresh water should always be available).
Do not give him scraps because they may spoil the puppy and put an end to the balanced diet you started with. But reasonably restricted treats should be fine (such as Milk Bone Biscuits).

2) Training
The best time to start training is when the puppy is five weeks old and older. You have to establish a teacher-and-learner relationship. Use praise and petting as reward. This a way to teach your puppy to obey the "sit" command:

Every time your pup wants to be petted, respond by holding your hand a foot above his nose and saying, "Dino (use your dog's name, of course), sit". Then move your hand over his ears as you speak. He will have no choice but to look up which should eventually lead to sitting. Keep repeating "good, sit" till he sits. Then pet him on the throat and chest with your other hand and repeat the phrase again several times. It may not work from the very first time so be patient and persistent, and - it is important - never ever get nervous. When the pup sits for about 5-10 seconds, release him but saying "OK" and pet&praise him again. Little by little, increase the time of sitting to 2-3 mins (before you say "OK"). It is also important that everyone in the house follows this procedure too.

These are just basic tips to start with, there is much more that can be said. I hope it helps! Feel free to ask more questions if you have any.