They are not a contract by themselves but they can absolutely be used to specify the details of the main contract the customer is about to enter, for example by buying something in an online shop, etc. and that contract is then in its entirety binding (assuming no laws are broken etc).

However, if Amazon included in their standard legalese a paragraph saying that they own my firstborn child that'd be considered null and void over here even if I click "agree", pay the purchase price for my order and everything, for the simple reason that it's not a thing you generally find in contracts about the sale of a bottle of fish sauce and a pair of hiking socks, and courts long since realised that noone actually reads fineprint. What they can and do put in the fineprint are things such as payment and shipment procedure details, that (in the case of buying on credit) the delivered items remain their property until paid, such stuff. Also on top of that the newborn child thing is against good mores which is another reason why it's null and void.

And Germany is a funny case when it comes to contracts, anyway. Say there's a shop advertising bubble gum for a euro a pack. That's a binding contract: Unless there's an obvious mistake (period in the wrong place or something like that), if I am an upstanding member of the general public and want to buy their bubble gum and they don't want to sell it I could go to court and force them to. Then, upon entering I take a pack of gum off the shelf and put it on the counter. That now spawns a sales contract, which spawns two other contracts: One obligating me, the buyer, to transfer property of money to the seller, and another obligating the seller to transfer property of the bubble gum to me. However, as I put an Euro right next to the bubble gum and unlike e.g. houses bubble gum packets don't come with registered ownership titles the two sub-contracts are fulfilled on the spot, which fulfils the sales contract, and nobody cares, except jurists and people making fun of jurists.

Non-verbal contracts very much are enforcable over here, the key factor is konkludentes Verhalten: Conduct implying intent. Long story short if you show up for work and the boss gives you tasks to do and you fulfil them you have an employment contract even though nobody signed anything.

Depends on your local laws. Verbal contracts exist here but they are unenforcable without a 3th party witness and even then very limited and only used for the simplest and most immediate exchanges. Buying and selling is kind of a contract but only handled in courts if it's between individuals, if a company is involved then it's the consumer protection laws and agency that handles that. Most obligations and privileges from buying and selling are handled by local law instead of a contract. But contracts on the Internet are only legally binding if you digitally sign it here, an agree button or even a normal signature isn't binding here for that. Our government IDs allow for online signatures with cryptographic keys unique to each person, that's the only legally binding online signature here.

A TOS can only be used to enforce your behaviour on that platform, anything beyond that is not enforceable here.