i have a cisco catalyst 1900 & i like to share internet among 15 PC in my lab they all are connected to the switch through a patch panel should i connect my ADSL Modem to the switch, the switch is running on default config.
If by modem you mean "router" you can attach the switch and it will allow your other devices to use the internet. The ISP will likely only allow you to have a single IP address. This is a generic limitation not related to the type of switch.
Although this switch will work it is more than 10yrs old. The best place for it is the dumpster. You are limited to 10m ports.