If you are attempting to do anything other than with straight pieces of tubing it might require the soldering thing. Plastruct makes "T" sections but they don't go much smaller than 1/8" diameter.
You can glue smaller diameter plastic tubing together in a "T" but the joint is not that strong.
If you are attempting to do small wire "T"s for things like brake lines or fuel lines then brass wire and some solder are the way to go. Soldering is quite easy. Some craft wire that looks like brass is not but is only coated and won't take to solder. So something like KS solid brass wire is best. Clean it well, add a bit of flux to the joint and touch the joint with a hot iron and some silver bearing solder. Only a small amount is needed to make the joint and keep cleanup to a minimum. The joint should be real shiny. If it is dull, that is a poor joint and will not hold. Hope this helps.