How do I make TF2 pyro type of weapon

[fervent acorn]

This is a two part question.
First I recommend using the gun handle for this.

To have 2 actions for 1 input device you'll need to determine how you want to set up the gun handle.
You could have short press (less than 1 second) trigger air blast and long press (over 1 second) trigger fire. Or the default press could be fire and "gun reloaded" could be air blast.
That's up to you but it is possible.

As for the flame thrower I'd recommend using a raycast from the end of the gun handle.
If the raycast hits a player within X meters away from the gun while the gun is being fired then apply damage over time.

Of course all these systems would need built but it's definitely possible to do!

[fervent acorn]

So your new to circuits?
In that case I recommend taking a class to learn the basics. Once you grasp the basics of circuits you'll better be able to understand what I wrote about.
Look in #class-info or on recroom.com/creative for class info!
There is a chance some kind fellow might come around here willing to teach you however I currently don't have the time to unfortunately.
If you have other small questions I'd be happy to help, otherwise best of luck!

Here's a few of the major ones

Get forward vector (of the gun handle)
Less than or equal too (to determine if a player is within burn rage)
A 30 htz to apply damage over time
Variables (float or int) to keep track of health 
Raycast (to get the player in front of the gun)