Good link for explaination og 5x5 lift

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Hi all,
I do some basic weights at the moment but want to do more.
Iv booked a session with someone at my gym but after looking further I dont think its needed.
Iv tried goggle but i cannot seem to find a good link that fully explains the 5x5 program.
Can someone help me out please?
Can someone from the uk recommend a good protein shake for me and the best place to buy?

Im also ordered Ne rules of lifting for women.

Thank you very much