Can i use my samsung galaxy y as a modem

There are application for hotspot wifi for android pones try one of those.

android should have wifi hotspot built into it already for free. the trouble is, most cellular companies disable it because they are greedy and want you to pay more for the ability (and they want to tack on extra data even if you have unlimited).

you have four options.

-use the free wifi hotspot toggle if your cell company does not block it.
-pay for the feature if it is blocked
-use an app such as pdanet for wifi broadcasting. it does have limitations though.
-root your phone and use a rom like MIUI which includes a wifi hotspot feature which is not blocked by cellular providers.

i wanted to use my phone as a mobile internet connection for my laptop and went through the whole process quite awhile ago. honestly the easiest and best way i found was rooting the phone and installing MIUI.

not only does MIUI give you wifi but it also has quite a few features not included stock. since it is aftermarket and not stock there may be quirks to work out.

ver 2.3 should be stable. ver 4.0 ics is in alpha mode and is still being perfected. not ideal perhaps, but i've had no more issues with this over stock.