Hello, repollo of repollo
Here's your question:
> How to connect to the internet using my dsl external modem
We don't know. It is extremely unlikely someone can advise you without knowing what modem you have there. I'd say even it is impossible.
Different modems require different handling. Some have PPPoE built in, some don't. Some have built-in routers and NAT. Some work over USB, some over ethernet. And so on.