I think this example should be self-explanatory:
using Plots; gr(dpi=600)
x = -π:0.1:π; y = atan.(x)
fs = 6
sp = plot(layout=(2,2), ratio=1, size=(800,600))
for i=1:4
plot!(sp[i], x, y, legend=:outerright, tickfontsize=fs, guidefontsize=fs, legendfontsize=fs)
end
lens!([-3, -2], [-1.5, -0.5], inset=(2, bbox(0.5, 0.5, 0.3, 0.3)), tickfontsize=fs-3, ratio=1, subplot=5)
lens!([2, 3], [0.5, 1.5], inset=(4, bbox(0.1, 0.1, 0.3, 0.3)), tickfontsize=fs-3, ratio=1, subplot=6)
plot!(sp, x->0.3*sin(10x)+1, c=:blue, subplot=6)
