Stratum detected a new block
Stratum is a protocol for miners, wallets etc to talk to nodes. It's not specific to Monero and it is used for other coins too. It's just informing you that the miner has started on a new piece of work.
accepted: 1/1 (100.00%), 320.07 H/s (yay!!!)
When miners mine in a pool, they're not working together. You're doing the same work as if you were mining on your own.
Think of miners going through a load of random numbers, doing "maths things" to them and seeing what comes out. If the number that comes out is greater than the difficulty, they've found a block (or a share). The problem is that the difficulty on the network is very high, most miners would never see a block despite all of the work they're putting in.
Pools give miners reduced difficulties, this means that not every share found is a block. If it's a block, it's mined by the pool and then all of the miners get rewarded based on how many shares they've submitted (and the difficulty of the shares). If it's not a block, the pool just gives you a thumbs up for trying and you carry on working.
I'm not sure if that was a terrible explanation or not, but to summarise, shares are just a way of miners to show that they are attempting to find blocks.
Also, I wanted to know how much block needs to be accepted to reach the payout of 0.5 XMR.
It's not possible to know just from the number of shares submitted, it also depends on the difficulty. You could submit hundreds of shares with a low difficulty and then still earn less than somebody submitting only a few shares with high difficulty.