Mouse over the buttons for an excessive amount of time and the tooltips will tell ya what they do.
Double click a table and go to "data" tab to see contents.
Schemas ->public is just a side effect of supporting a lot of different databases. Many support schemas
Ram is because default java heap size, you could probably change launch params to get it much lower though.
On all counts other DB tools I've used are just as obtuse and burn tons of resources. Most are written in Java or another high-level language because it's nigh impossible to get DB drivers for a ton of different databases working together in C. DBeaver is basically leveraging JDBC for what it was designed for