Hey,
First of all: Great to have you here and happy to see you starting out.
I would highly recommend you check out the Flow-Designer. Flows are very similar to workflows, but they are a bit easier to design (please check with your team architect, if flows are an option instead of workflows). Next, check out the servicenow developer material! It will give you a great introduction to both flows and workflows! You can find that here.
To answer you specific question:
You are looking at actions which require a split and then a "wait for" action. The split goes in front of your approval. One path creates the approval, the other one enters the "wait for". Behind the "wait for" you can then put an action to trigger a notification. Repeat that for the next notification as well. Then join that path with the approval (this does not make a lot of sense, but its as you described. Ideally something else should happen here, e.g. a different approval for the manager of the original approval -> an escalation).
Then you can join your paths. The way joined paths works is - if not configured differently - only one has to finish. E.g. if your workflow finishes even though the "wait for" path is still running, that gets aborted.
Note: This is the most rudementary way of doing this. There are more elegant ways, but start out by doing this. You can do the same with a flow instead of a workflow.
Regards
Fabian
