Restare vs. riposare
The Italian words restare and riposare are often confused by learners, but they have completely different meanings. Restare means to stay or to remain, while riposare means to rest or to relax. They are not interchangeable.
Restare
A1This verb means to stay in a specific place, to remain in a certain state or condition, or to be left over. It implies a lack of movement or a continuation of a state and has no connection to physical rest.
Stasera resto a casa a leggere un libro.
(Tonight I am staying at home to read a book.)
Dopo la discussione, siamo restati in silenzio per un'ora.
(After the argument, we remained silent for an hour.)
Del dolce è restata solo una fetta.
(Only one slice of the cake is left.)
Resta calmo e raccontami cosa è successo.
(Stay calm and tell me what happened.)
Sono restato sorpreso dalla sua reazione.
(I was (remained) surprised by his reaction.)
Quanti giorni resti a Roma?
(How many days are you staying in Rome?)
Riposare
A2This verb specifically means to rest, relax, or sleep in order to recover from fatigue or effort. It is about ceasing an activity to regain strength and energy. It is often used in its reflexive form, riposarsi.
Dopo il lavoro, mi piace riposare sul divano.
(After work, I like to rest on the sofa.)
Il medico mi ha detto che devo riposare di più.
(The doctor told me I have to rest more.)
Lasciamo riposare l'impasto per la pizza per due ore.
(Let's let the pizza dough rest for two hours.)
Durante la gita, ci siamo fermati per riposare le gambe.
(During the hike, we stopped to rest our legs.)
Non fare rumore, il nonno sta riposando.
(Don't make noise, grandpa is resting/sleeping.)
Vai in vacanza per lavorare o per riposare?
(Are you going on vacation to work or to rest?)
Summary
In short, the difference is fundamental: restare is about location or state (to stay, to remain), while riposare is about activity (to rest, to relax). You restare in a hotel for a week, and during that week, you riposare by the pool.