这两个都是现在分词作状语,说明时间
现分一般在连词之后作状语,也可位于名词前后作定语
作状语时,表主动.可转为相应的从句,如：After giving me a letter,Tom went back to his desk.=After Tom gave me a letter,Tom went back to his desk.
作定语如：a man sleeping in my bed.睡在我床上的男人.
动名词相当于名词在句中作主,宾,表成分.
如：i like swimming.
swimming 就是动名词,作like的宾语.