Users confused about what syntax they should use within the issue filter

Related to: #25913 (closed), #27326 (closed), #26928 (closed)

When conducting usability testing (#26945 (closed)), 4 users were confused about the syntax they should use within the issue filter. [Clip 1] (https://youtu.be/RQGV7y-6uoQ?t=15m30s), [Clip 2] (https://youtu.be/wbz-0Kii4jM?t=6m41s), [Clip 3] (https://youtu.be/wbz-0Kii4jM?t=7m4s), [Clip 4] (https://youtu.be/cF0CS-rcpZU?t=2m11s), [Clip 5] (https://youtu.be/cF0CS-rcpZU?t=3m25s), [Clip 6] (https://youtu.be/UF_zfCYgukw?t=9m27s).

How can we make this easier for users?