First, let me be clear. No one expects you as a parent to be able to help your kid with their chemistry homework. You probably took chemistry a long, long time ago or not at all. Do you honestly remember any of it? I would assume not. Its not your job to actually sit there and tutor your child in how to do some complex chemistry problem. It's part of their education to figure that out.
Your job as the parent is simply to remind them that they need to do it. Offer support to them and offer guidance by perhaps pointing out certain resources but don't try to do their homework for them. When teachers say, "get involved!", they simply want you ensure that studying and doing homework is emphasized in your home. That's all. No teacher expects a parent to sit down with their kids and work through some complex math problem for advanced algebra. They simply want you to make sure your child tries to do it.
If they struggle with it, that is ok. Sometimes things are hard. Sometimes the answers don't come easy. Don't stress out about the fact that you need to be able to figure out the answers. You don't. The teacher will help them. Your job as a parent is to simply make school a priority.