I'll let @bmogilefsky describe the jobs. @18F as a whole hires engineers, designers, product managers, content writers, journalists, folks with non-traditional cross-functional backgrounds, etc.
Salary depends on job grade. See [1] for an explanation of the grades within 18F. Then see the GS pay scale [2] to figure out the pay for your grade in your region.
[1]: https://pages.18f.gov/joining-18f/pay-grades/
[2]: https://www.opm.gov/policy-data-oversight/pay-leave/salaries...