As per the docs I linked to in my first reply.
Which provides an example request:
curl -H 'Authorization: Bearer cfabdegwdoklmawdzdo98xt2fo512y' \
-X GET 'https://api.twitch.tv/helix/users?id=44322889'
The header is Authorization and you should preceed your token with Bearer since you provide a Bearer to can omit ?id=Whatever