Best way to Asakusa from Shinagawa

Hello, I have been to Tokyo before, but only using the Yamanote line. I really want to go to Asakusa next time, but I'm not exactly sure how the transferring procedure works.

Since I believe none of the subway lines in Shinagawa station goes to Asakusa, I see that the Tamachi station does have the Asakusa line.
So would it go something like this:

From Shinagawa - buy a ticket for Tamachi station via Yamanote, and then at Tamachi buy a ticket for the Asakusa line to Asakusa? Or is it possible to buy both tickets at once at Shinagawa?

Thank you

There are some direct trains from Shinagawa to Asakusa along the Asakusa Subway Line, departing from the Keikyu platforms of Shinagawa Station. You will have to purchase one "transfer ticket" at a Keikyu ticket vending machine of Shinagawa Station.

There are also various alternative routes that require one transfer along the way. Most of them will require you to purchase two separate tickets, one at Shinagawa Station and another one at the station where you transfer:
http://www.jorudan.co.jp/english/norikae/

Or you could use a prepaid card:
http://www.japan-guide.com/e/e2359_002.html

You can easily get from Shinagawa to Asakusa - the Keikyu line goes through Shinagawa on up, though it changes its name somewhere and becomes the Toei Asakusa subway line.

At Shinagawa station, follow signs to the Keikyu line, but you'll have to buy another ticket - and it's a pain there, because you have to actually go to a window and speak to a person to buy a ticket. There always seems to be a line, though the ticket people are fine with english.
But if you use Passnet or Suica you can use it on Keikyu as well as JR.

People will help you get to the right platform. No worries.