1. Is ripple decentralised really... i mean for instance with BTC no single person can just pull the plug because the don't like it.
What about ripple? if the people that created ripple wanted to, could they shut off their servers and ripple is gone?
No they can't, all(!) code to operate Ripple now and in the future is open source and free software:
https://github.com/ripple2. It is closed source right because i guess it would have been cloned by now?
Nope.
https://github.com/rippleIt took years(!) until someone created the first Bitcoin based altcoin and they never gained real traction.
3. why do i have to trust people to let them send me ripple? this seems really weird, i mean if every time you want to get some ripple you have to trust them....well just seems strange.
Sending XRP is the only thing that can be done without trust, every other transaction on Ripple requires you to state where the thing you are trading is actually stored/held in escrow. Bitcoin exchanges usually don't require this distinction, since you are usually only able to trade balances on the one and only platform you are currently using (you can't trade BTC you have deposited on Kraken for USD on Bitstamp for example). An exception could be for example localbitcoins, where you might see different prices for people sellling BTC for PayPal vs. bank transfers.
4. i have heard people say already over and over again.... it can already be used to exchange any other crypto? ...how though? how do you exchange doge for qrk or vert to doge over ripple?
You find a gateway to store your Dogecoins (e.g. Peercover), deposit them there and then trade on Ripple for whatever you want to have. You then either keep what you bought as balance on Ripple or withdraw it from the issuer you specified when buying the other thing (could be for example Bitcoins on Bitstamp, ounces of gold from RippleSingapore...).