Hello there and welcome to Swift! 
I usually handle our (the swift projects) gsoc participation, so I can answer some of your questions.
It is too soon for the 2026 projects, we’re wrapping up 2025 right now and the next chance to apply will be next year. You should check the program timeline ( Google Summer of Code 2025 Timeline | Google for Developers ) and keep an eye for the 2026 schedule. Generally, projects are announced somewhere in February or March.
You should start out by reading all the contributor guides on the summer of code website Help | Google Summer of Code and also posts of past contributors. This year we have two posts already:
- [GSoC 2025] Bringing Swiftly support to VS Code
- [GSoC 2025] New JNI mode added to swift-java jextract tool!
Their projects were selected from Project Ideas for GSoC 2025 | Swift.org and there will be a similar page in 2026. But again, there isn’t yet, because it’s too soon
Hope this helps!