#NotStandardGerman is full of modal particles (in German also Abtönungspartikel), small words which describe how the speaker feels about the content of a sentence. Today, we will look at 4 of them: “ja”, “halt”, “eben” and “mal”.

2/ The particles are hard to acquire for learners of German, first because no one really knows how they work and second because they look like words which more concrete meanings. They are not obligatory in the strict sense but so common that you will sound way more native-like.

3/ “ja”: you know this as a positive answer to questions. As a modal particle it expresses that a speaker assumes an information as already known to the listener.
„Ich hab Peter ein Buch geschenkt, er liest JA sehr gern.“ → both speaker and listener know Peter and his hobbies.

4/ But “ja” is now also often used when no such shared information can be assumed. Instead the speaker highlights that something is or should be common knowledge or shouldn’t be questioned. The sentence above can then be read broadly as “reading is a good thing”.

5/ And other speakers use “ja” simply to structure their sentences and use it after every new information.

6/ “halt” and “eben”: these two words are similar in that they express that the speaker either wants to mark unpleasant unformation as unchangeable or that something is mere background information (or both). “halt” is a little more colloquial than „eben“.

7/ “Am Wochenende hab ich wenig Zeit, ich muss HALT/EBEN viel lernen.” → implication: “I can’t change it” and/or “that’s the reason but it’s not really important what I’ll do”.

8/ You see that the two words have nothing to do with the meaning of the similar sounding words “halt” (‘stop’) and “eben” (‘flat’/’level’). “eben” can also mean that you do something quickly and in the near future: “Ich geh EBEN einkaufen.”

9/ “mal”: this is similar to “eben” in the latter meaning
“Ich geh MAL einkaufen.” → implication: “I’m going to do it soon and quickly”.

10/ “mal” is also similar to “eben”/”halt” in that it expresses that this is background information and not so important. For example, you would shout the sentence above if you are leaving the house and want to inform your housemates that you are gone now.

11/ Notice that this thread only reflects my personal intuitions about the meaning, I looked up if they match the literature (they do) but other people may use these words differently.
Oh, and you can combine particles (but not all of them): “Ich geh HALT MAL EBEN einkaufen.”

12/ Btw: have you ever noticed that some speakers of German make overly frequent use of words like “just” when they speak English: that’s because they miss their modal particles. Now you know that “I’ll JUST go shopping.” is a translation of “Ich geh MAL einkaufen.”

Translations (I tried):
3/ I’ve bought a book for Peter, you know, he really likes to read.
7/ I have few time on the weekend, (by the way) I just really have to study a lot.
9/ (By the way) I’ll just (quickly) go shopping.
11/ (By the way), I’ll just quickly go shopping.