The simple answer is about what you'd expect--a relatively uncontested French advance by the army of the Pyrenees into the heart of Spain in 1795 forced the Spanish crown to sue for peace (with minor territorial concessions in the Caribbean but otherwise just a cessation of hostilities).

To put things in the broader context of the War of the First Coalition, the victory in Spain was one of many lightning successes that had a sort of domino effect of quickly (and unexpectedly) tilting the conflict in France's favor. After the French overran the Dutch republic in the Netherlands and established a client republic in its place and forcing the kingdom of Prussia to conclude peace the same year, the Austrian Habsburg empire rapidly found itself the only major coalition power still in the field (Great Britain was involved as well, and would remain at war with France even after the collapse of the First Coalition, but their involvement during the initial war was limited to a blockade and a few failed attempts to harass the French with abortive coastal raids).

The victories were impressive and boosts to morale in their own right, but just as importantly, each enemy knocked out freed up additional troops to support the fight against the republic's more determined enemies. The forces that were no longer needed for the war in Spain were then able to bolster Napoleon's spectacular efforts in the Italian campaign, which would ultimately result in Austria's surrender in the treaty of Campo Formio and the end of the First Coalition.

Source: The Oxford History of the French Revolution, William Doyle.

Edit: Grammar fixes.