I have tangent snap on. I have an arc, then I draw a 2nd arc with Start/End/Included, start is the end of the 1st arc, end in somewhere, I can adjust the arc but it does not snap tangent to the 1st arc. How to make the 2nd arc tangent to the 1st arc?

That's not how it would work.  Just because you are close to an arc with another arc doesn't mean that there is a Tangent solution to be highlighted.

Better to use the Tangent to Arc or Curve or one of the others.


Jeff

My drafting skill is not good, sometime tangent snap is useful to me.

Attached dwg is an example created in Rhino, TC2018 can open it. I attach screen shots of how tangent snap in use, one is Rhino, another is BricsCAD. Is there a equivalent way in TC?

As Jeff says there are special arc tools for this purpose.
Sometimes I use construction lines and arcs to set it up.
 the centre of both arcs and tangent point would be in a straight line.

I used "Circle Tangent to Entities" for this exercise. I activated the tool and 'no snapped' near the end of the Arc to establish the tangent. Now I activated the "Through Point" option and Vertex snapped that same endpoint, then Vertex snapped the endpoint of the Line. A circle is created between the Arc and Line, that is tangent to the Arc. Use "Object Trim" to remove the excess area of the Circle.

My arc comes out the same as yours.

Many thanks for the detail steps, I tried the same circle command before but failed to do it because I didn't know the "Through Point" option. Now I can create the arc without tangent snap, of course it will be good if TC implement tangent snap in future which save a few clicks.

Many thanks for the detail steps, I tried the same circle command before but failed to do it because I didn't know the "Through Point" option. Now I can create the arc without tangent snap, of course it will be good if TC implement tangent snap in future which save a few clicks.

see attached video
 is this what you're looking for?
I used once click snaps, to show what snaps were being used.

I think it is not a tangent snap, the arc length is different, the guide is a circle and not a line, that's the problem I think.

I think it is not a tangent snap, the arc length is different, the guide is a circle and not a line, that's the problem I think.

see attached video 
It works,it's just a precision thing,it's tangent to the arc.
You imported geometry,it wasn't native TC  ,it could be anything.

I found using Tangent to entities no need to trim, the Through Point is a great tip.

I found using Tangent to entities no need to trim, the Through Point is a great tip.

Good to see that you've got it working with the Arc tool. Having two defined points is a big help. I rarely run into a situation where the "Arc Tan To Entities" would work without some trimming afterwards, so I always go with "Circle Tan To Entities".