There are two different types of animation blending in Track View: Cross-Fade blending and Gap-Blending.
This blending method automatically kicks in if two animations overlap each other. The blending affects the whole section where the animations intersect – the "weight" of the second animation will steadily increase towards the intersection's end. At the start of the 2nd animation the weight for the first/second animation is 100/0 and shifts linearly until the end of the first animation to 0/100. See the illustration below:
This blending method can be used to blend from the end frame of one animation to the beginning frame of the next animation.
To enable it, you have to set the "Blend Gap" option of the FIRST animation to true. Also for the system to be able to actually blend something you need to keep a gap (hence the name) between both animations.
Half a second proves to be a good value for most blending operations, but you can choose whatever size (= blending time) you want.