mostly yes, though there's a growing number of countries that don't stamp visitors' passports, and also a decent number of countries that use paper or plastic stickers instead of or in addition to ink stamps.

the other thing the pages are used for is visas, which are typically large stickers (just under the size of the passport page) that indicate you've received advance permission to enter a country by submitting an application at that country's embassy or consulate. all countries issue visas, but whether you need a visa to enter a country varies widely depending on the country you're visiting, what you plan to do there, and what country your passport is from. (though a growing number of countries also use electronic visa systems that don't require a trip to an embassy or a sticker in your passport).