How to analyse an ECG?
First bump is called P point, middle is QRS wave (as in Q-down, R-up, S-down), and last bump is T. Every feature is representation of electrical activity in certain region of heart. E.g. P bump is contraction of atrium. See more here. Bumps are P/QRS/T.

The reason why you see so many different recordings is that it was taken with many-lead ECG. Heart has very distinct shape, its atrium is on top of ventricle, it is a bit tilted to the right, etc. Your recording is a projection of electrical activity vector onto vector that connects two leads used for given recording. Pick two other electrodes and you will have different picture just because axis of projection changed.



via NIH

It seems to me that recording you show are from different pairs of electrodes, but it shouldn't matter. As you can see, different pairs of electrodes will "pick up" some processes better that the other.

Now, because ECG is electrical activity recording, heart rate is least useful information to extract from it. Measuring pulse will be less of a hassle and as accurate. But what you can do is estimate biophysicals properties of given heart. For example, distance between P and QRS (PR interval) complexes is time that it takes for heart to contract ventricle after atrial contraction. Any abnormalities will cause lengthening of PR or other change. Lengthening of PR interval often indicates 1st degree AV block (AV node is not conducting as usual).

There is bunch of information out there on ECG and abnormalities, you can find useful this page from U Utah with examples of many severe conduction abnormalities.