@albert73  All you do is click the Like button and it will change from “Like” to “Liked” if you are looking at the button on the Facebook Page.  Usually people want you to Like it from your personal profile so it “counts” toward the overall number of Likes for their Page.  If you are Liking their Page from your Page, it doesn’t count towards their “Like” count.

But my philosophy is you should only Like pages you are genuinely interested in or you want to show support for.  If I”m just Liking the page but I’ll never buy anything from them, I don’t think it matters.  Personally I’d rather have 500 fans who may buy from me than 50,000 fans who will never buy from me.