0 to do someone else's work for them because they cannot or will not do it themselves: --
She will fill in for him while he's at the conference.
1 to do someone else’s job temporarily: --
The gym teacher was sick today, so a substitute filled in for her.
2 to write or type information on a document in spaces that are provided for it: --
4 to tell someone something they do not know, especially something that happened when they were not there: --
We can complete it step by step however long the road is and it can't be completed however short the road is if you don't even mark your footprint.
Vi kan slutföra det steg för steg hur lång vägen än är och den kan inte slutföras hur kort vägen än är om du inte ens markerar ditt fotavtryck.