I feel your frustration there. This is not well explained by any of the wallets yet, either in documentation or through the user journey on the apps (in my opinion)

Conceptually, the beads on the abacus metaphor was most helpful for me initially. 

When you open a channel (i.e. fund your wallet), all the beads are on your side.

Someone sends you a payment, if there are no beads on their side the LSP opens a channel to you on your behalf on the fly. This hits the chain therefore result in mining fee.