If you're trying to control the width of a cell on a report, in Text-Mode you can add the code:
usewidths=true
width=400
And then just adjust the number (in my example, 400) to be the width that you'd like to set for your column.
If you're trying to limit the amount of text returned in a cell, try something like this in Text Mode (which I got from one of @moniqueevans example reports):
valueexpression=IF(LEN({lastNote}.{noteText})>350,CONCAT(SUBSTR({lastNote}.{noteText},0,349),"...(open for more) --"),IF(LEN({lastNote}.{noteText})>0,CONCAT({lastNote}.{noteText})))
In the above example, if the length of the note is more than 350 characters, the formula will only display the first 350 characters followed by "...(open for more) --"