I am planning on playing a campaign, and I want to play a gold half-dragon. I haven't found any information about how I would create one, and what abilities it would have. Is it canon?
There is no playable race for Half-Dragons
There simply is no player race for half dragons. There is however a half-dragon NPC template in the Monster Manual, here is the intro to the section:
A beast, humanoid, giant, or monstrosity can become a half-dragon. When a creature becomes a half-dragon, it retains all its statistics except as noted below.
Challenge. To avoid recalculating the creature’s challenge rating, apply the template only to a creature that meets the optional prerequisite in the Breath Weapon table below. Otherwise, use the guidelines in the Dungeon Master’s Guide to recalculate the rating after you apply the template.
This template is designed to adapt existing NPC statblocks to half dragons. Jeremy Crawford sums up the half-dragon rules nicely in this tweet:
Jason Evans: How are the FR half-dragon monsters related to the dragonborn race? Seem similar except for the tail.
Jeremy Crawford: Dragonborn are a race, whereas half-dragon is a template that can be applied to certain creatures
Jason Evans: Thanks. The illustration of half-dragon champion at the end of Ep1 of ToD looks like dragonborn with a tail. Confusing.
Just reflavor the existing Dragonborn race.
All is not lost, however. The half-dragon template added to a humanoid NPC produces a character mechanically similar to a Dragonborn, so I would recommend simply reflavoring the existing Dragonborn playable race to be half-dragon, half-whatever. This produces a playable race thematically similar to what you’re looking for, but mechanically identical to the existing Dragonborn playable race.