Firstly, you need to make a new composition to your clip, right clip on you clip, go on composition settings then increase the time to allow you clip to be slowed down and still fit in the allotted time.
Then you need to drag this newly created composition down into the left hand corner of the composition box third from the left. it look like a square box with a circle, a triangle and a square in it.
You then need to click on the dial below that shows 3 video tapes, and when you hover over it should say enables frame blending for all the layers with the frame blend switch set. Then go to layer - frame blending - Pixel motion, then go to layer again - time - and enable time remapping.
The you need to go to effects - R.E Vision plug ins and select twixtor. Now with twixtor applied to your extended composition, in the very bottom right hand corner that extends the length of the bottom of the window, you need to go to your clip, press the triangle on the right to reveal effects, transform and audio. Then press the triangle beside effects, and press the triangle beside twixtor.
Then go to output control and click the triangle beside that, and go down to speed. using the time line located were you want the twixtor to start and leave the orange marker were you want it to start. A couple of frames before, put the marker there, then go to speed. There should be a stopwatch, click that and it should leave a triangle on the time line a couple of frames before were you want to put twixtor. with the triangle inlace, then put your orange dial on the time line were you want to slow down, and go to speed and reduce the speed. this will make the twixtor occur from that point.
Hope that helps !!..