Tinker's tools let you make basic repairs and craft temporary items
The Player's Handbook doesn't provide much information about each type of tools other than its name; aside from thieves' tools, players and DMs were left to largely figure out for themselves how to make tool proficiencies relevant. However, Wizards of the Coast finally provided some more specific guidance on how tool proficiencies could be made useful with the release of Xanathar's Guide to Everything
Xanathar's Guide to Everything (p. 78-85) adds guidance on tool proficiencies, providing both general guidance on how tool and skill proficiencies might work together and specific guidance on each kind of tool. For each kind of tool proficiency, it lists the components of that set of tools, relevant ability checks that proficiency with that tool might grant you advantage on if you're also proficient in the skill, a special use of the tool for those proficient with it, and sample DCs for activities the tool might be used to perform.
Tinker's tools are described on p. 84-85:
A set of tinker’s tools is designed to enable you to repair many mundane objects. Though you can’t manufacture much with tinker’s tools, you can mend torn clothes, sharpen a worn sword, and patch a tattered suit of chain mail.
Components. Tinker’s tools include a variety of hand tools, thread, needles, a whetstone, scraps of cloth and leather, and a small pot of glue.
History. You can determine the age and origin of objects, even if you have only a few pieces remaining from the original.
Investigation. When you inspect a damaged object, you gain knowledge of how it was damaged and how long ago.
Repair. You can restore 10 hit points to a damaged object for each hour of work. For any object, you need access to the raw materials required to repair it. For metal objects, you need access to an open flame hot enough to make the metal pliable.
The activities the tinker's tools could be used to perform in the table after that include "Temporarily repair a disabled device", "Repair an item in half the time", and "Improvise a temporary item using scraps".
Thus, it is clear that tinker's tools are quite limited in what they enable you to do. They don't let you make anything you can dream of (such as a plane or parachute, even assuming your character could conceive of such a thing); they simply let you fix up small things, and potentially jury-rig a temporary replacement for something that breaks. Think (a limited version of) MacGyver, not some futuristic scientist/inventor hybrid.