Clays and mud are available for ceramics and pottery, sand for glass, and there is a tremendous variety of organic materials available for chemical industry -- dyes, acids, drugs, etc. Stone masonry is quite possible, since concrete can be mixed that can set underwater.
Submarine oil deposits may be found in sedimentary strata. Natural gas and other combustible vapors upwelling from the planetary interior could be trapped in special containers and burned using oxygen imported from the surface. Lacking combustion, bubblewheels could be erected over regions of submarine helium gas effluence and the rotary power used to turn mechanical flywheels.
Tools underwater would be much different than we think of them. For example, swinging a lever like an hammer or axe, is not efficient under water because water resistance robs all the energy. Plus, rapid high energy motions stir up silt and generate vibrations that telegraph one's position.
Instead, grinding, raking and drilling would be the orders of the day. Repetitive motions over short ranges would work better than rapidly moving levers. Water jets, with or without injected abrasives, could take the place of knives and saws.
Various forms of bicarbonate and biosilicate would likely take the place of stones. Likely, a form of coral topiary would be an early technology on par with making mud bricks was for humans.
It's important to remember that you don't need as strong of materials to build underwater as on land.
Sonics carry for hundreds of miles in the oceans and can carry multiple bands at the same time. Even at very primitive levels, they might coordinate millions of individuals over tens of thousands of hectares with the ease of which humans coordinate a small village.