This is clarified in Xanathar's Guide to everythingXanathar's Guide to Everything. Essentially, most of what the Herbalism Kit does is act as a supplement to other abilities. The examples given in Xanathar's GuideXanathar's Guide are using your knowledge of nature to assist with Arcana checks relating to plants and potions, assisting with Investigation checks relating to looking through anywhere with overgrown plants, assisting with Medicine checks when using herbal remedies, and so on.
Most of the kits in the game don't have an obvious list of things to do with them, and work like thisthe same. They are mostly roleplay opportunities for your character to shine in a specific way. If you're stuck in a forest and need to determine which plant is which, you would mention to your DM that you have expertise in plants due to the Herbalism Kit, and likely would be given advantage or proficiency bonus on the roll, if not just be told outright immediately.
No. Instead, whenWhen you craft an item, the items that are used for that craftingto craft it are factored into the cost.
You could roleplay this as saying that your character replenishes anySo yes, while you technically use some of the consumed items as part of this costkit to create the item, you simply replace the parts that you used afterwards.
Page 130 of Xanathar's Guide to Everything covers the specifics of Potion of Healing crafting. ItIn summary, a basic Potion of Healing takes a day of downtime, 25gp of materials, and anproficiency in (and access to) the herbalism kit.
Technically speaking, you don't. Crafting an item in 5th edition handwaves all of that part of the craftingmaterials and resources by simply charging a variablean amount of gold depending on what it is you are crafting and just says "you buy what you need".
Your DM may rule otherwise, and were I the DM of your game and you wished to spend time gathering the herbs needed rather than simply buying them, I'd happily allow that as a roleplay opportunity. You spend more time doing it, but need to spend less gold. However, that's up to your DM, and would be homebrew rules.
This is another situation where it is up to your DM. Your DM will need to present you with the opportunity to tell what type of herb the given plant is, and you would mention to your DM that you have Herbalism Kit proficiency so you would be able to identify it. You can also mention it on your own, as well; if you are in an area with potentially valuable/helpful herbs or plants, ask your DM if your character could search for and gather something useful.
While not part of your question, there's a line in your question that is concerning and should be mentioned to a beginnerfirst-time player as you mention you are.
The thing with D&D is that the DM is the one who runs the game. The rulebooks are secondary to how they want to run things. If they've agreed to be DM, then they've agreed to also answer rules questions when they come up. To do otherwise is just plain silly; he's the DM. That's the job he accepted when he chose to become DM. If he doesn't want to answer rules questions from his players, he shouldn't be DM.