I’m ok with it only being 10%. 
Well, I guess it depends what you’re comparing it to. It takes 3 days for a bank transaction to clear, bitcoin is certainly faster than that. Anyway, there are lots of innovations in the pipeline to speed things up. For example, the lightning network will enable sub-second transactions by moving them off the main blockchain and settling them afterwards.
The same way they’re stored now. Miners secure the blockchain by building blocks, which include user transactions. Space on the block is limited however, so users can include in their transaction a fee for the miner to motivate them to include theirs earlier. The rules of the protocol also allow miners to include a special transaction for themselves, which is the mined bitcoin. The rules also specify how big this mining reward is each time, and when it will end. Once it does, the miners will continue their work but their source of income will be exclusively transaction fees. The rationale is that while the network is small they need the extra motivation of the mining reward, but by 2140 (when the last new bitcoin is mined) the network will be large enough to be self-sufficient.