Hi, I am so sorry I am new so I don't know how to work this properply yet. So, I don't know if you are suppose to ask question about something that might be specific to me but this is the only thung i found to as my question. 

My question is, are suppose to start at the note C3 when we are doing basic or advance lip trill slide exercise or is it a based on your own preference kind of thing?

and also,  do the instructor always starts at C3 note when they say C major key?

and what id you are a tenor but can't reach C3 yet.

P.s. sorry for my name I am just not that confident yet, plus i am very shy.

If we're starting in C major and the exercise pattern starts on "1" (for example: 1-2-3-2-1), then "1"=C. 

If it's more comfortable to start on C4, you can sing 1 octave higher and then rejoin the lower voices when it's comfortable again!

If you're not singing with a lesson video, or if you're accompanying yourself, you can start wherever you're comfortable.

Glad to have you here. Welcome!

thank you...

You're welcome!