If you haven't seen the in-game instructions, they're worth reading if you're not familiar with Minesweeper and the genre that this prototype draws upon. The introductory video here on the game's Itch page also explains the game's concepts if that's helpful.
1# What do the numbers mean?
The numbers on each tile indicate how many fossils are adjacent to that tile. The game is about observing the numbers and deducing the locations of fossils so that you can safely dig around them and avoid destroying them.
2# And why sometimes you dig 1 tile and other times its 5-7 tiles that get done with the single click?
It is an established genre convention that if you dig/reveal a tile that has no adjacent items (such as explosives, or in this case, fossils), all adjacent tiles will be automatically revealed. Since the gameplay is entirely focused on using the numbers for logical deduction, tiles without numbers serve no purpose, and removing them reduces the tedium of clicking on unimportant things.
Each generated dig site has a difficulty, which determines the density of fossils. Easy dig sites will have more opportunities to reveal large areas with one dig. Hard dig sites will have less.
3# When do we get to assemble the parts? i did the Australia site and after finding all bones it seemed all i could do was leave?
Once you have excavated or destroyed all of the fossils in a dig site, the dig phase is over, and you must return to the main menu.
From the main menu, you can either select another dig site to hunt for more fossils, or you can click the "Build skeleton" button. Skeletons must be constructed from the feet up. If you have not found any foot bones, the option will be disabled and you will need to visit more dig sites.
If you would like to assemble skeletons without digging for fossils, you can click the "Build skeleton (practice)" button at the main menu. Skeletons assembled in practice mode will not be added to your inventory and will not be available in the showcase.
All dig sites are randomly generated. In a "full version" of this game, certain fossils would only be found in particular regions, but for this prototype, the location names are purely cosmetic.
Hope that helps.