imagine my phone rings and I see ...

it's someone I know well

then I can answer it and simply say 'Yes?'

personally, I find that a bit unfriendly

and I also think it sounds a bit annoyed

so I never answer the phone like that myself

but I've certainly heard it done before

I think it's better to just say 'Hello'

and if you don't know who's calling ...

or don't know the person well ...

you answer with your first and last name anyway

so if someone's name is Anna Mayer, she'll answer and simply say 'Anna Mayer'

if you listen to native German speakers speaking ...

you'll notice that we sometimes just say 'JA' at the beginning of a sentence

while we're telling someone something

'JA' doesn't then really have its own meaning

but simply connects the sentences

and helps keep the flow of the conversation

for example: 'Yesterday we were at the lake and had an ice cream

'JA', and then it suddenly started to rain'

'JA' is like a filler word here without any real meaning of its own

or imagine that I want to explain to a colleague

 ... how something works on their computer

I say: 'You have to open this program first

'JA' and when it opens, click here ...'

this 'JA' is, of course, only heard in spoken language. It's not written down

imagine: you're sitting in a meeting with your colleagues

to prepare a presentation for an important client

colleague A suggests showing a long presentation first

and then discussing it with the client

colleague B doesn't like this and says ...

 'I think it would be better if we incorporated short discussion sessions in between'

colleague A reacts: 'No, we won't do that, that's nonsense!

the client needs all the information before we can have a discussion'

Colleague B then says, 'It was just a suggestion'            

he uses this 'JA' here to weaken his own statement'

he is trying to say: 'Hey, I didn't mean to interfere or provoke you

I just wanted to make a suggestion

it wasn't meant to be malicious. You don't need to react so irritably'

here's another dialogue: 'Are you coming to the park this weekend?

'no, you know very well I don't have time at the weekend'

'it was just a question'

'I'm saying, 'Hey, I'm sorry, I don't want to start an argument

I just wanted to ask you a simple question

you don't need to react so emotionally. I didn't mean to provoke you'

this function of 'JA' is probably the most difficult for non-native speakers to learn

I suggest you pay close attention to how native speakers use 'JA'

you'll probably notice that it's used quite often