When you create the purchase invoice (Purchases >> Enter New Purchase), this can contain all the detail you want. You can keep it as basic as “Stock”, or you can list each item on the receipt/invoice - the choice is yours.
You can also attach documents to each invoice, so if you wanted to keep it simple, you would still have the backing document in case anyone asks any questions, like HMRC.
Generally these would be tagged to a purchase invoice so they’re linked to the correct supplier. For example:
There are a few ways to create a purchase invoice, including:
- Go to the Purchase menu, and select Create new purchase
- Create it through tagging (as you’ve shown in your screenshot)
Each method creates them slightly differently. By doing it direct through the purchases menu, you can enter as much detail as you need. If on the other hand you have lots of tagging to do, you could use tagging to create the invoice (like how you’ve shown). This is however limited to a few characters and will only record a 1 line purchase invoice.
So it depends on what level of detail you want, depends on how you can create them. I would suggest giving them all a go and seeing what works best for you.
But to answer your question regarding General Purchases, this is a COG code and will be treated as such. You can view a full list of the codes by going to Reports >> Chart of Accounts.
Office Equipment is balance sheet code and will flag it as an Asset. For something like ink, I would go for Hosting Fees & IT Consumables.
If you create these through the Create a new purchase option, then there’s also an option to help you find the correct category 
It’s no problem! It’s why we’re here.
We also have this article in our knowledge base which gives a full run down on credit cards. You may find this useful: