The inbound and outbound journeys are not extra. It's just that on 2 of your travel days, you can also travel in your country of residence. You can then also use as many trains as you like, but only on 2 travel days.
I don't quit understand what you are trying to say but you can use your Interrail Global Pass
in 33 countries EXCEPT YOUR OWN COUNTRY* in the partecipating train companies, to use a train you need to add the trains on the app or write on a paper pass. You will also use a travel day for that. A travel day goes from midnight to midnight CE(S)T. If you enter a train before midnight and you exit the next day ot will count only one day.
* You can use in your country the pass on two days, but this days are not extra to the travel days.
If you have still some questions feel free to ask.
Les jours dans ton pays de résidence ne sont pas des jours supplémentaires. Tu as juste le droit de voyager 2 jours sur 10/15/etc. dans ton propre pays.
Tu peux très bien faire Paris - Lyon et retour la même journée. Il faut juste noter que la SNCF a instauré une réservation obligatoire pour les TGV (et Intercités) : 10€ (limité) puis 20€ jusqu'à ce que le TGV soit complet.
Ces frais s'additionnent vite en Espagne, France et Italie...
Tu peux bien sûr emprunter les TER sans payer les 10 ou 20€