A happy day!

I am fond of photography.  Every friend konws knows my interest1. I got received a gift from my best friend.It's - a tripod!  It's worth costs $512. Is it very this cheap?  Although it is a cheap gift,but I think it is represent our friendship! Even if it is, I don't care for it is the thought that counts! 3

I will use the tripod  it in all my travels. It would be like having my best friend beside with me. 4 I will take more photos with my camera!

Your English is pretty good.  Just needed some finer points in good writing.

1.  If I were you, I would replace the word, "interest" with "passion".

2.  Is this US$ or RMB?  I don't it is cheap if it is in US$.  Here's an idiom you can use in this situation: "Don't look a gift horse in the mouth"

3.  From the way you write, it can also mean hidden sarcasm - meaning you have a cheap best friend and that your relationship is just like the cheap tripod - cheap.  So if your friend is in a bad mood, he may think you are sarcastic and angry that he had given you something cheap.  This way, it is clear and no other way of interpretation.

4.  Your sentence seems incomplete and lots of blanks to be filled by the reader's mind.  This would make your writing better by giving it more warmth.

A happy day!

Today was the best! OR I was very happy today!

The sentence you wrote was not complete.  It had no verbs. 

I am fond of photography.

I enjoy photography. 

Using the word fond is okay, but enjoy is used more often to describe hobbies.

Every friend konws my interest.

All my friends know of this interest.

Friend should be plural.  Use this interest because you are talking about your interest in photography which you already mentioned.
I got a gift from my best friend.It's a tripod!

My best friend gave me a gift.  It was a tripod.

Instead of being passive (got from) you should be active (gave).  Since it was in the past, use the word was
It's worth $51.Is it very cheap?Although it is a cheap gift,but I think it is represent our friendship!

It cost $51.  Is this inexpensive?  Although it is inexpensive, it is a sign of our strong friendship.

Use cost when you bought something whose price you know.  Use worth when you are trying to guess how much it should cost.
I will use the tripod in my travel.I will take more photos with my camera!

I will use the tripod when I travel and take more pictures!

use when instead of in

~Nicely written.  I understood what you were trying to say.  Keep up the hard work and take great pictures!