Perhaps a demonstration will be clearest:
julia> a = Ref(42)
Base.RefValue{Int64}(42)
julia> b = a
Base.RefValue{Int64}(42)
julia> a[] = 69
69
julia> a
Base.RefValue{Int64}(69)
julia> b[]
69
julia> b
Base.RefValue{Int64}(69)
julia> a === b
true
An important bit to note is that a Ref needs to be deReferenced to get the value using the b[] notation.