Is this your first contribution to Open Source? If yes, please read the excellent first time contributor guide at https://opensource.guide/how-to-contribute/.
Generally, we welcome contributions from volunteers. A number of improvements we'd like to see implemented are listed at general/docs/contributions.md in addition to the issues tagged with "helpwanted". But we're happy to consider anything you'd like to contribute. However, some parts of the tlaplus repository follow a very strict contribution policy. So before you start working on anything, please discuss with us what you want to do. You can do that on the issues page. We do not want to reject your 1k LOC patch because the actual change is not considered sensible by us.
Except for TLAPS, the TLA+ tools are maintained in Eclipse. For instructions on how to setup the Eclipse IDE, please go to general/ide/README.md..
We collect quality metrics. If you want to help out with the project, the reports indicate several low hanging fruits to pick.