1日怎么说用英语

"1日" means "one day" in English. You can say "one day" to refer to a specific day in the future or in the past, or you can use it more generally to refer to a typical or average day. For example:
I'll see you in one day. (specific day in the future)
One day, I hope to visit all seven continents. (more general, indefinite time in the future)
One day, I woke up to find that it had snowed overnight. (specific day in the past)
I usually spend about one day per week volunteering at the animal shelter. (more general, typical or average day)