stepping stone
noun uk/ˈstep.ɪŋ ˌstəʊn/ us/ˈstep.ɪŋ ˌstoʊn/
(STONE)
[ C ]（溪流或河流中的）踏脚石，垫脚石
one of a row of large, flat stones on which you can walk in order to cross a stream or river that is not deep
(STAGE)
[ S ]进身之阶;敲门砖，垫脚石，跳板
an event or experience that helps you achieve something else
I see this job just as a stepping stone to better things. 我只不过把这份工作当作找到更好的工作的垫脚石。