USE: three cells straight upward
Trace USE from U at row 5, column 3. Move up to S at row 4, column 3, then up again to E at row 3, column 3. Both moves stay in the same column, with no sideways step and no turn between the start and finish.
This is one straight segment spanning three rows and one column. Its starting cell has one open orthogonal neighbor, while its final cell has four. That difference helps you check the direction: start with the U and finish as soon as you reach the third letter. The extra open neighbors at the endpoint do not add letters to this three-letter answer.
The first entry accounts for three of the board's 19 open cells and leaves 16. Keep the S and E tied to the positions just traced; the board contains other copies of both letters. Confirming this entire vertical segment gives you a specific completed path to carry forward.