You have three options. Let's see the example with this command:
get-mailbox | format-table name, primarysmtpaddress, distinguishedname
Probaly the distinguishedname column does not fit into the screen.
First you can do is use the -wrap switch for format-table:
get-mailbox | ft name, primarysmtpaddress, distinguishedname -wrap
This will wrap the all the 'cells' of information that does not fit into its column. The problem with that is - as in this example - other columns have more space unneccessarily. So the second option is to overwrite the default columns widths:
get-mailbox | ft name, primarysmtpaddress, @{n="distinguishedname"; e={$_.distinguishedname}; w=70}
With this hashtable definition I set a new coulmn that has the same name as the original one (n=...), even the data is the same ({e=...}) but has a new width (w=...).
The third option is to output the result to the gridview:
Get-Mailbox | Select-Object name, primarysmtpaddress, distinguishedname | out-gridview
In this new grid window you can adjust the columnwidth by the mouse.
