。
When I try to walk, I get a sharp pain right here.
Literal
Walk try-to [when-と] here [subject-が] throb-does (polite).
Three pieces worth noticing. (1) 歩こうとする ('try to walk') uses the volitional + とする pattern for 'attempt to X.' (2) ~と after a verb is the conditional 'whenever X, Y' — natural consequence. (3) ズキンと is a mimetic (擬態語) for a sharp, throbbing pain — one of Japanese's many specialized pain mimetics (ズキズキ for continuous throbbing, ピリピリ for tingling/stinging, ヒリヒリ for a burning sensation). Combined with the adverbial と and する ('do'), it becomes the verb ズキンとする ('throbs sharply').