I'm assuming a PC. Go to your control panel. Find the "clock, language, region" and select "change keyboard". Add "US Internatinal". There will then be a little keyboard icon on your menu bar. Use that to toggle between regular and US int. keyboard. On the International key board you type the sequence 'a to get á. You use the little blip under the tilda and the a to get à. You will have to type a space after an apostrophe to get an apostrophe.

Look here: http://italian.typeit.org/