I want the user to be able to buy gift cards for any amount. I also want users to be able to use gift cards as an alternative means of payment.

I have updated to eCart6, and have now started using this.

Based on your eCart tutorials, I have customized my product catalog and shopping cart as I want it (it should be a booking system for a company offering drink tastings).

The next step is to create gift cards. Here I want the user to be able to buy gift cards for different sums. I also want users to be able to use gift cards as an alternative means of payment. How do I do this?

I have started looking at your guide: eCart Coupon series, and suspect that it is one of the tutorials that are not created (4 and 5), I should start from. Sad, because now it feels like I'm "on the move", so to speak - with this!

Since this project is a way for me to learn how to create a shopping system, I have chosen not to get paid from this customer. Therefore, unfortunately, I can not buy any consultant for this.

But if anyone could help me complete this, I would have been very grateful. Ideally, I'd like to do this on my own, starting from WebAssist's excellent tutorials.

I would work through it step by step and ask specific questions here when you get stuck.

The steps would be something like:
1) Allow customers to purchase gift cards and add them to a shopping cart
2) Save gift card purchases to the database after checkout so they can be retrieved later
3) Display a gift card balance for purchased gift cards
4) Allow users to apply gift card balances to shopping carts
5) Reduce the "amount" available in gift cards when they are used

This is going to be rough for you to pull off on your own, but it is possible. I think #5 is probably the most difficult step, but don't get too caught up in worrying about the next step. Do each step and work through your issues and whittle away at the problem and eventually it will be done.