So yeah, it places a bet on augur, buying as many shares as it can for "no trump wont be elected" which are currently around 90c and will resolve to $1 in January when biden is sworn in. The reason it isnt $1 yet is because some people are buying the other side of the market for whatever reason. It seems like an obvious bet really, so the strategy is to pool everyones money, take the bet, and then after the market resolves pay back the winnings to the pool.
This particular strategy is just a bet. but other strategies would involve borrowing assets and lending them out to gain interest like you mention. You could say "i can do that myself, what is gained by pooling" and there are two things: 1 you dont have to manage this, the strategy keeper manages their strategy and takes a small fee to do so, and 2 you would be in competition with the pool, less lenders means higher rates so it makes sense to pool the lending.
They get increasingly complex involving taking insurance, lending, borrowing, producing tokens, burning tokens, etc. all from other decentralised protocols, it all gets stitched together across platforms. Money lego is a phrase often used, but really its more like `npm install insurance`
Ah sorry about the link, didnt realise (btw you dont need a yearn account, there is no accounts on these platforms, but you probably do need a web3 wallet like metamask. you have a wallet and that is your account across all platforms, so you hold your user data with you, and can have as many identities as you like for each platform).
Another link to read more on yearn specifically is Andre's blog (creator and one of the lead devs) https://andrecronje.medium.com/ it is one of the interesting projects as it is growing organically, with a mix of public and anon devs, with no specific management, and no VC investment behind it (like some other defi projects), just people coming together an building interlinking code as public goods.