Jamming against missile threats is always done on the type of seeker head employed by the enemy. This information is usually onboard and stored in the EW suite's computer so they know what to look for.

You can, as already described in above posts, jam in various methods. Most used are:

Range Gate Capture jamming (RGC) which effectively takes the radar "ping" of the missile and creates a false return later in "time" (and stronger signal-2-noise ratio) than it is receiving the ping thus making it look like the target is actually further away from the missile's viewpoint. This method is to make sure the missile doesn't arm itself, thinking the target is further down the road.
This type of jamming can also be used with a phase shift, bending the target's ghost location away from your own position. This way the missile might go seek in a different angle and the original ship falls out of the missile seekers search cone.
Basically what you do is to create a false target for the missile.

Spiking is to jam 1 threat at a time by bombarding it with white noise, it's the same as described above by turning on a loud radio next to someone's ear who tries to listen to a return of a noise he made.

Noise level increase. Imagine what the radar seeker sees, a lot of clutter below the horizon (the sea) and above it emptyness. When a "spike" or " spot" appears on the horizon, it's a target, meaning, worst case.. you.
By increasing the "sea clutter" artificially, you can create such a high clutter zone, missile seekers won't even notice you because they can't detect you anyway.
This works wonders on sea-skimming missiles. Basically you increase the clutter so much, you immerse yourself completely in it, drowning you out from the missile's seeker.

On ship-2-ship EW, like the TS questioned, I can only say the first one to fire up its radar is the one getting detected, recognised and classified in a blink of a second by todays EW systems. Once they have a range, it'll be a matter of time to get distance info.
Jamming a shipborne platform isn't widely used as we're talking ranges of around 20nm... that's an unhealthy distance for 2 ships that do not like each other to be in. But if push comes to shove, they'll employ a barrier or spike type of jamming to either mask their global position, course and speed from the other side or push out so much noise that you blind the other side completely, call in an airstrike, maintain jamming until missiles are released, go outside and watch the fireworks.


These are just examples, there are offcourse more ways to jam incoming threats.
Hope you enjoyed reading it :)