Purely extended formulas like CH3-CH2-CH2-CH3 showing bonds aren't very convenient, but are doable. You can just draw butane (zig zag, or draw it linearly) then use the text tool to click on each terminal line or junction and label it with "CH3" or "CH2". Then select the entire structure and pick Flush Left (or something other than Automatic) under the TEXT menu. THEN you want to go back and scoot the carbons around. Turn off Fixed Length and Fixed Angle (under the menu OBJECT). Then select the single bond tool, then Shift-mouse down on a carbon and you are free to scoot and shift it to where it looks good. See, not the best. Remember the text tool does understand alkyl groups (phenyl groups, abbreviations, etc), so you can type on an atom "CH2CH2CH2CH3" and you get a nice butyl _group_ on something.
First in preferences->general be sure your measurements are in inches. Then under view->Show crosshairs). In the pallet select "drawing elements" (it looks like a box with a shadow) chose the line. Then just draw. You will measure the length with the grid you see on the page.
You can get a trial version at perkinelmerinformatics.com/products/research/chemdraw/ but just a word of warning, the purchase price is pretty high (crazy expensive, actually).
