Thanks for your interesting question about amber. This substance, ancient tree sap, is preserved in sedimentary rocks that formed in a terrestrial (rather than aquatic) environment.

In certain places, sedimentary strata that originally formed above sea level (some of which contain amber), have been pushed--by various geological forces--below sea level. Suppose an amber-containing formation is currently exposed on a shoreline. Wave action and other forces weather away that rock body, leaving behind tougher residue, such as amber.

Amber is generally less dense than water, so it floats. Therefore it sometimes washes up onto beaches, where it can be found by people who know what they're looking for--kind of like finding "sea glass" (polished pieces of broken glass) on beaches in our area.

Amber can also be found on land, in areas where it's preserved. It can be recovered by carefully surveying the surface of the ground, by sieving, or through small-scale mining operations.

I hope this answers your question. Amber is really cool stuff, particularly since it's a great source of fossils, particularly those of insects (which got trapped in the originally sticky sap).

Many minerals end up on beaches, because water erodes and transports rocks and sediment grains.

Both rivers can erode rock and deposit it on beaches. Amber in particular has a density that is similar to seawater and can occasionally float in it, so it tends to accumulate near the edges of saltwater bodies. Since amber can only be transformed from tree resin to mineral underground, the most direct way to get it is mining. What you find on beaches is amber that has been exposed by water. Major sources of amber include Russia, the Caribbean, and Southeast Asia.

Amber is a type of rock that is formed from the resin of trees that hardens and gets buried. It can only be found on beaches because there is rock near the beaches that is being eroded or torn up from the seafloor by waves, and that rock contains amber.

Amber-containing rocks can be found all over the world, and are usually from about 140 million years ago or younger. Obviously these rocks also need to have been formed from sediment that was laid down where trees were growing at the time, so rocks formed under the ocean or volcanic rocks do not contain amber.

Amber on the sea floor washes up onto beaches during big storms.

Wikipedia says amber can be found anywhere:
"Pieces of amber torn from the seafloor are cast up by the waves and collected by hand, dredging, or diving. Elsewhere, amber is mined, both in open works and underground galleries."

“Dripping resin can sometimes trap seeds, feathers, and even animals such as ants or mosquitoes in its viscous goo. Not all resin becomes amber. Organic substances such as resin are usually broken down by weather (such as extreme temperature changes or rain) and decomposers in the food web (such as bacteria and fungi)”