Sortir is used when the subject leaves a place.

L’oiseau est sorti de son oeuf.

On the contrary, partir is generally used when it implies the destination.

Il est parti en France pour l’été.

We can use partir without a destination. In that case, it will mean that he left for a long moment.

Sortir and partir do not have the same meaning.

• Sortir means getting out of something in this context. A physical object or an abstract object is needed.

For example, “je sors de chez moi“, or “de la fumée sort de la cheminée“, or also “l’accélération est sortie des valeurs limites de sécurité, c’est pourquoi la fusée s’est auto-détruite“.

When no object is specified from here, from where the subject is currently should be assumed: “je sors. (d’ici)” or “attention, quand je dévisserai ce bouchon, du liquide va sortir (du réservoir)“.

• Partir means to leave a place, or an entity, in this context. A destination may be specified.

For example, “je pars deux semaines en Espagne cet été“, or “Jean a démissionné, il est parti chez un concurrent“, or also “Stéphanie est partie ? (de cette réunion)“.

• In certain cases, this is subtle:

Stéphanie est partie ? suggests she left the party, or the meeting, for good

while

Stéphanie est sortie ? suggests this is temporary: she will be back in a while

In English, partir is to depart (or leave). Sortir is to sortie, (or go out of). You can go out of something (e.g. a house) without leaving the general vicinity.

McWhorter, J. PhD Linguistics (Stanford) bruits three meanings unique to sortir, on p. 151 Bottom of Our Magnificent Bastard Tongue (2009).

  How does it sound when it’s French that has one word where English has more, and when it isn’t something as immediately evident as the European know verbs? In French, sortir means “go out,” but also covers what English would express with come out (in the earthquake, le tiroir est sorti de la commode, “the drawer came out of the dresser”), get out (someone is in a hole and says, “Sors-moi d’ici!” “Get me out of here!”), and stick out as in one’s tongue (“Sors la langue,” “Stick out your tongue”).

Les deux verbes n’ont pas le même sens: ”Sortir” c’est statique, changer de décor encombrant, de coquille, de cachette, se défaire, se libérer d’embarras, tandis que ”partir” c’est se déplacer à quelque part pour de bon, le plus souvent sans revenir au lieu de départ.