Help understanding items

This is an extremely basic question, but I have not been able to receive an answer. What should your gameplay involving items look like? How many do you purchase with starting gold? How many consumable items? Do you restock those? How often should you buy new items? Only when you die? Should you ever go back to base in order to spend gold. How bad is missing gold value? In what order? That's a lot of questions, and I can't expect answers to all of them, but confusion regarding items is really the only thing holding me back as a new player of the game. Thanks for the time and consideration, should you choose to answer.

Firstly: What game mode are you playing? Purchasing in Conquest vs. Arena is usually quite different. Based on your questions, I'm going to assume you're talking about Conquest, if not, ignore most of what I'm about to say.

Before anything else, I have to say that there's no shame in autobuy. When you're first learning how to play the game, I found it best to worry about getting my gameplay up to snuff first and learning items second, so I would only proceed to learn itemization once you feel you've at least gotten the hang of a few gods and a few roles.

Generally with starting gold, every position is going to buy a starter item. (In this list, the first starter item is generally the preferred one): As support, you're typically looking at either Watcher's Gift or Mark of the Vanguard. Mid laners (or mages in the solo lane) grab either Vampiric Shroud or soulstone, ADCs grab either Death's Toll or Bluestone Pendant, Solo lane Warriors will almost always grab Bluestone Pendant, but may grab Death's Toll and Junglers will always take Bumba's Mask. These items give you a stronger early game and are generally worth the 800g. Most roles will also take some Healing Potions and Mana Potions as well as the first tier of their first or second item (eg: mages will often start with a starter item, Lost Artifact (tier 1 of Chronos' Pendant) and some health and mana pots, most Hunters will start with a starter item, and either Spiked Gauntlet or Morningstar, etc). Junglers and supports are an exception to this; it's popular to start supports with a starter item, Creeping Curse and health and mana pots and junglers with a starter item and either Boots or potion of physical might as well as health and mana pots. Finally, most players will sell their starter item at some point so that they can upgrade another item (it's usually best to hold onto it for your first 3 items at least though).

Consumables are a whole different territory. Firstly if you haven't heard by now, you should be buying Wards every time you go back to base. You can only have 2 out at once, but they are invaluable to gaining knowledge on the enemy team's whereabouts and preventing yourself from being surprise ganked. Aside from that, you should only be buying healing potions and mana potions when you really feel you need them. Using money on consumables can get expensive if you're not careful about it, so try to only buy them when they're a necessity rather than a luxury.

Generally you should buy new items whenever you go back to base or die. You should go back to base either when you've run out of health or mana and need to replenish those stats, or if you've racked up enough gold to purchase a full item (if you see you have 2000-3500 gold, you should consider going back to base).

As for your last two questions "How bad is missing gold value? In what order?" I'm not sure exactly what you mean. In any case I hope this helps!

By missing gold value, all I meant is should I aim to be spending 100% of my gold whenever I am in the shop? The other question is less relevant now. Thanks so much for taking the time to answer this!

you should buy as much of an item you planning to buy as possible and if you need 10 gold (or another small amount) you can wait for it in base.

Also health pots can be useful all game long because it allows you to regen if you are playing someone without a heal or good lifesteal. or during fights to keep you alive a little bit longer.

If you want to have the best handle you should get on items the way to look at it is every game look at what your biggest concern is for instance if the enemy mid laner is getting fed a stone of Gaia or a bulwark of hope start sounding better and better. Or if they have several basic attack oriented gods midgaurdian Mail becomes a great option or say you start getting ahead and know your team will be getting in kills then a hide of the urchin is an amazing item. Or say you are not dealing enough damage. So on and so forth. That's how I look at items