For holding the choke cable sleeve to that bracket with the screw hole, a top half-moon bracket goes over the cable sleeve and is tightened down by a screw into the top half-moon bracket and then into that screw hole on that bottom bracket you have. There should be a small half-moon depression in that bracket below the choke cable. The top half-moon bracket will squeeze the cable housing between the top and bottom half-moons. You can make one easily if you can't buy one.
Where the top of the choke cable goes into the handlebar thingie, it should just screw up into the housing. I believe the screw part is separate from the tube and turning the nut will screw the tube to the handlebar thingie. Just don't cross-thread it.