When it rains, the water flows over sediments, rocks, and minerals. These materials dissolve a LITTLE bit; these dissolved ions are carried to the oceans and build up over time.

When rivers flow over rocks, they erode the rocks a little and pick up some of the minerals, including salt, that were in the rocks. The rivers eventually meet the oceans and slowly bring salt to the oceans. This happens very slowly over long periods of time.

Rocks - rocks have salt in them, if only a tiny amount. Water dissolves salt, and water runs downhill and collects in the ocean, and then evaporates to make clouds - leaving the salt behind in the ocean. Over the eons, this has caused more and more salt to arrive in the oceans and stay there, so the oceans have become salty.

Great question! Salt gets into the ocean by the weathering of rocks on land. Salt is a mineral that contains the elements sodium and chlorine. Both of these elements are found in rocks and are easily dissolved and carried in water. The interaction of rain and groundwater with rocks causes some sodium and chlorine to go into the water. Eventually the water makes it all the way to ocean basins, and it carries the sodium and chlorine with it. That is why the oceans are salty.

Because of the water cycle, water gets evaporated from the ocean and comes down as rain in the mountains. The rain eventually flows back down to the lowest point, which is usually the ocean. On the way, it dissolves minerals and salts from the rocks and soils, and takes that with it to the ocean! Over the several billion years this process has been happening, that adds up!