1. Calculating the age of the Universe
If you convert Hubble's constant into SI units then you can use this to calculate the approximate age of the Universe. A common exam question (since much of astrophysics is long answer questions): You will need to know how to carry this out this procedure.
2. The Big Bang
This started everything - space, time and eventually all of us. This is where our 'normal' physics can't really describe what happened but we can look at the evidence as we now observe the night sky.
3. Evolution of the Universe
There's a lot in this video that explains everything ever! Basically as the Universe expands it cools down, the quarks combine to make hadrons and eventually atoms. Take notes - there is a lot of information here.
4. Derivation of Critical Density
Do you need to know this derivation? No. Is it useful to see where the equation has been derived from? Yes. This is why the critical density is related to big G and also Hubble's constant.
5. Fate of the Universe
What will eventually happen to the Universe? There are a few possibilities and these depend upon how close the density of the Universe is to the critical density. Open, flat, closed or even accelerating?