Since Ismail is not a standard Unicode font, the keys on your standard QWERTY keyboard will map differently to Tamil characters.
If the font is in a ZIP folder, right-click and select "Extract All." Install on Windows: Right-click the Ismail.ttf file. Select Install from the menu. Alternatively, drag the file into C:\Windows\Fonts . Install on Mac: Double-click the font file. Click Install Font in the Font Book preview window. Technical Specifications