We don't really have enough info to help you out, is not clear what you mean by "difficult to install agricolae", what error message do you get when you run install.packages("agricolae")? also, what do you mean by "various windows"? on which version are you?
Could you ask this with a minimal REPRoducible EXample (reprex)? A reprex makes it much easier for others to understand your issue and figure out how to help.
If you've never heard of a reprex before, you might want to start by reading this FAQ: