The third type of character is "two components that are put together to give it meaning". For example, 明 which in the word 明天 means tomorrow, comes from 日 the sun and 月 the moon put together. If you have a day with sun, and then night with moon, then you have another day - tomorrow. The other meaning of 明 is "bright".
The fourth, and by far the most common type of character, is when one part gives the character its meaning and one part gives a character its pronunciation, which I believe are called phonosemantic compounds. Basically , some characters that all look really similar have similar pronunciations - watch this for reference https://www.youtube.com/watch?v=B8joWLPGaTA
. 請 情 清 青 精 靖 婧 晴. These are called a phonetic series. The 青 is pronounced "qing1", and all others are related to this pronunciation, but their other components change. Watch the video, it explains it better. There are others, too, like 喝 遏 謁 揭 歇 偈 is another set that springs to mind. Can you see how they all have a common component?
Anyway, bearing in mind that some characters have sound components, where does the meaning come from? There are things called "radicals" in Chinese. A radical is a "meaning component" to a character. For example anything with 疒 suggests illness 病 疾 痼 痠 etc. Basically, after you have enough characters, you might be able to guess how to pronounce a character. 鸚鵡 is the example I use. 嬰兒 means baby and is pronounced "ying1 er2", 武器 means wepon and is pronounced "wu3 qi4". 鳥 means bird. You can from this guess that the pronunciation might be ying1 wu3 (or something similar, they don't always match up perfectly like this one) and it is a type of bird. You'd be right! 鸚鵡 means parrot.
Does that make more sense now?
Oh, the best way of memorising characters is simply writing them by hand over and over again.
Best of luck in learning Chinese!