how to make whats on my computer show on my t.v.

You haven't given much information on what you have so here goes.

There are a few ways to do this:

HDMI port on the TV? If so, get a miniDP to HDMI adapter and connect to the TV via HDMI cable.

DisplayPort on the TV? If so, get a miniDP to DisplayPort cable and connect to the TV.

DVI port on the TV? If so, get a miniDP to DVI adapter and connect to the TV via DVI cable.

Then go into system settings and mirror the display.

I'm presuming that you've already made the connection with a suitable cable. What are you getting on the TV? Are you getting a completely blank screen? Are you getting a message similar to 'no input detected'? Or are you getting the spiral galaxy desktop?

If the last of these then what you have is an extended desktop. If you move the mouse cursor off the edge of the MBP's screen you will see it appear on the TV. Similarly you can drag windows from the MBP's screen to the TV. At present the MBP's screen is the primary display and shows the menu bar and dock, and the TV is the secondary display. To change this go into System Preferences -> Displays -> Arrangement. You will see an image of two screens, a smaller one representing the MBP's display and a larger one representing the external display. At the top of the smaller screen in the image is a bar, this represents the menu bar at the top of the screen. Drag it from the smaller screen to the larger screen. The external display will become the primary display and the menu bar and dock will appear there and any new windows or applications that you open subsequently will appear there too.

silvergc's suggestion to use mirroring will work, but you won't be using the native resolution of the TV which could result in fuzziness or bluriness of the image on the TV.