Basically a Lightning connection (or channel) is two parties locking up some money (in any amount and any split they want) and then repeatedly re-agreeing on what the current split is. At any time they can close the channel which unlocks the money according to the latest agreed split. It's cleverly set up so that if either one cheats (by trying to finalize an earlier split), the other one gets to overrule it and keep 100%.

The most money that can be transferred is when the split is 100% to one party. Then you need to finalize it and create a new one.

It's not as magical as its proponents think. It is better than the base protocol in some cases - if you have connections and money. The sender having to lock up actual money in advance, in the maximum amount they can foresee sending, is a real buzz killer for the sender. And if the sender is some central relay - if you want to receive via a central relay and not peer to peer - you'll have to convince them why they should do that. Usually by actually prepaying, in real bitcoins, a few percent of what you want them to lock. Which is more than the transaction fee for a nontrivial base layer transaction.