How do you get a picture off your camera onto instagram?

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For my birthday which is very soon in about a week infact, i am getting a canon camera as one of my gifts.
Now I follow many people on instagram and they have pictures that they have taken with their camera on their instagram, even if its just landscapes, their pets, a picture of them or a picture of them in the mirror with the camera. And they write in the description taken with my canon camera so on...
And i'm not going to lie, I am quite a big fan of instagram as many are and when I have my camera I am going to want take pictures off their and put them onto instagram, but I have never got how you do that.
Do you have to put them into your photo libary first? Or straight into instagram, even so I don't know how to do that.
I have an Iphone 4 by the way incase that helps because it might be different for other phones.
Thank you