Students we talk to end up not using the manual very much, for this reason we don't send out the manual with the calculator. But we do provide the download for each of our calculators.
Most of the time your teacher will be able to help, but there are cases where having the manual is the only way. Just by right clicking on each of the calculator names below you should be able to download the file. As you right click, go to "Save link as..." to download the pdf onto your computer.TI-83 Plus TI-86 TI-84 Plus TI-89 Titanium
Free Online Graphing Calculators