want 2 learn about graphics

Topic is a bit wide, but il include info that may help you be able to figure it out on your own.



There is more to a graphics card than just their generation, at various points AMD and Nvidia trade blows within the current (600/7000) gen. What might be more helpful is an explanation of their naming schemes.

There is a Pre-fix to the name the specifies which line of graphics cards it belongs too. For mainstream gaming cards, AMD use the "HD" prefix and Nvidia use the "GTX". They also have brands names like "Radeon" (AMD) and "GeForce" (Nvidia).

AMD
I'l be using an AMD 7850 as an example
The first number (7850) indicates its generation and architecture.
The 2nd number (7850) indicates its performance tier within the graphics card lineup. The low end is 7, mid-range being 8, with the high end being 9.
The 3rd number (7850) indicates its rank inside that tier. The bottom is 5, the top 7. If there is a 9, it indicates it is a dual GPU card (except for the 7790, which really should be called a 7830).
Last number means nothing, its always 0.

Nvidia
These guys have a naming scheme thats a bit easier to comprehend.
The first number (670) indicates its generation.
The 2nd number (670) indicates its ranking in the whole graphics card lineup. Ranges from 1-9 with it being more powerful as you go up. If its a 9, that means its a dual GPU card.
3rd number is always 0.
Sometimes there is a Suffix like "Ti" on the end of the number, for all intents and purposes you can just consider it a new card altogether (better than the non-Ti version). I suspect Nvidia did this because they ran out of numbers.

Using that you can see which cards from AMD and Nvidia are supposed to be pitted against each other, but thats only in the naming scheme, actual performance comparisons need to be taken from benchmarks.

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The eternal question of which there is no answer, because the answer changes all the time. When Kepler released (GTX600) you would have been mad to go AMD. Then when AMD responded with an aggressive price drop , they were back to equal. Then AMD launched their Never Settle bundle alongside a massive driver update, you would have been mad to go Nvidia. Now the GTX700 series is coming out, and until AMD respond with their new cards you would be mad to go for AMD. When AMD drop the Volcanic Island GPU's (HD9000, not 8000 as makes sense) then you would be mad to go for Nvidia.

All comes down to when your buying and at what price tier, because one never has the outright advantage over the other.