For this week, the first character is that of 門 (mén), which means "door". The etymology of this character is very simple: the ancient form of this character is only simply a picture of a door.
The second character for this week is completed by adding the 亻 radical, from 人 (we looked at this in week 1's lesson). If you then add the 亻 radical, from 人 (we looked at this in week 1's lesson), to the left side of the character 門 you will end up with the character 們 (men), which is used to turn a pronoun into its plural form.
In terms of an equivalent, you have the singular pronouns of "I", "you", and "he / she / it". In Chinese, we would write these as 我, 你, and 他 / 她 / 牠 / 它. By adding 們 to the pronouns, you change them into the plural form, so 我們 is "we", 你們 is "you", and 他們 / 她們 / 牠們 / 它們 is translated as "them".
You will also remember from week 1 that we discussed the fact that the third person pronoun in Chinese uses different words depending on the subject matter. The same rationale will also apply to the plural pronouns.
The third character this week is more of a historical one. Although the title of this lesson has this character as 尔 (ěr), it has in the past been written as 爾, which is more obvious when considering its ancient form.
Another way this character has been written before is 尒, which as you can see is closest to the form featured in the title of this week's lesson,
尔. The character can be used to mean "like that", or "that", for example 爾時 would be "that time", 爾日 for "that day". Another meaning of the original character, which has now been replaced by the next character for this week, is that of the second person pronoun, 你 (nǐ), meaning "you".
The forth character this week is 你 (nǐ), which I have already mentioned. This character actually used to be written as 儞, but as you can see from the above how 爾 has developed to 尔, so it follows the same pattern that 儞 had in the modern day incarnation developed to 你. The 亻 radical added to the left side of 尔 denotes some reference to people, which is handy for remembering that it is the second person pronoun, "you".
In light of how this character has shifted from its original form, it's probably best just to memorise how this character is written considering the small number of strokes (only seven strokes).
The final character this week is very simple, coming in at only three strokes. The character 大 (dà), meaning "big". This character is a depiction of a person (人) with outstretched arms. It had also been written in the past as 亣, which looks like a stick figure with a small head, outstretched arms, and legs slightly apart.