None of those are genuine Deans connectors for a start, if they were they'd be a lot more expensive. Try component shop or a decent RC supplier.
Fitting them is relatively easy as long as you have a decent soldering iron and a steady hand.
Tinning as mentioned above is the process of flowing solder onto the parts to be joined prior to actually soldering them together. When it's done right it produces a far better join with less probability of getting a dry joint (where the solder doesn't flow properly and you get a mechanical joint with poor electrical conduction). I always tin the connector and the end of the wire before joining them but I learned how to solder in the aerospace industry...
As SD mentioned, don't forget the heatshrink, don't cut both battery wires at the same time and the socket always goes on the battery.