using Plots should import the plot function, after which you can not get that error. So that is where things go wrong at least; the Plots package is not properly loaded into your workspace
now I am getting this
ArgumentError: Package Plots [91a5bcdd-55d7-5caf-9e0b-520d859cae80] is required but does not seem to be installed:
Run Pkg.instantiate() to install all recorded dependencies.
Stacktrace:
[1] _require(::Base.PkgId) at .\loading.jl:999
[2] require(::Base.PkgId) at .\loading.jl:928
[3] require(::Module, ::Symbol) at .\loading.jl:923
[4] include_string(::Function, ::Module, ::String, ::String) at .\loading.jl:1091
[5] execute_code(::String, ::String) at C:\Users\Administrator.julia\packages\IJulia\rWZ9e\src\execute_request.jl:27
[6] execute_request(::ZMQ.Socket, ::IJulia.Msg) at C:\Users\Administrator.julia\packages\IJulia\rWZ9e\src\execute_request.jl:86
[7] #invokelatest#1 at .\essentials.jl:710 [inlined]
[8] invokelatest at .\essentials.jl:709 [inlined]
[9] eventloop(::ZMQ.Socket) at C:\Users\Administrator.julia\packages\IJulia\rWZ9e\src\eventloop.jl:8
[10] (::IJulia.var"#15#18")() at .\task.jl:356
Then I would reccomend doing what it says - it is generally a good idea. Make sure to run using Pkg first, so that you can use the function with the suggested command