These words are called “correlative conjunctions.” Like their counterpart coordinate conjunctions, they link grammatically equal parts. The word also can be moved to later in
the construction, or it can be omitted entirely.
…not only John but also Bill…
…not only John but Bill also…
…not only John but Bill…
When these link two sentences, there is a comma before but also. When they link dependent construction, there is no comma.
…Not only did I see him, but also I had a chance to talk to him.
…Not only were we together Friday, but we also spent Saturday together.
…I went to not only France but also England when I was there.
…Not only Marilyn but also Joan decided to join us.