I am new to stats and have a couple basic questions regarding sampling , the central limit theorem and probability.

If the sample size is 30 or greater then the sample means follow a normal distribution.I wanted to know the minimum size of the observations in each sample and its limits. Can I take 30 samples each having 2 observations with the knowledge that the means of these samples would follow a normal distribution?

Also I would like to get an intuition about probability distributions. What is the fundamental difference between probalility distruibutions and frequency distributions?

Can anyone please let me know about these as I am not able to progress much without getting my basics clear

Thanks

Viv