Question: Sum of multiple terms

Hi, I have numerous terms all of the type opl[i]:= ... with i an integer . Now I want to calculate the total sum of all these terms. I've already worked with a commando like: "for i from 1 to 4 do opl[i]:=... end do;" but I can't find a way to make the sum of multiple terms. By the way is there a site of a good handbook where I could learn more about programming in Maple and make animated curves or objects?
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