How can I find out the screen resolution and dpi on my mac book pro?

This depends on the model of Macbook Pro (i.e. the screen size - 13.3", 15.4" or 17") you purchased, but the resolution and DPI (or PPI), for the 2009 unibody models, is provided by Wikipedia (here and here).

However, given the resolution and display size, you can easily calculate the PPI. In summary:

MacBook Pro 13.3":  1440x900 (127.68 PPI)
MacBook Pro 15.4":  1440x900 (110.27 PPI)
MacBook Pro 15.4":  1680x1050 (128 PPI)
MacBook Pro 17":    1920x1200 (133.19 PPI)

Open the Apple menu at the very top-left of the screen and click on About This Mac. Click on the More Info button, which will open up a window with lots of categories of information. The Graphics/Displays category will tell you your screen resolution.

If you like terminal, then you can get via below command

system_profiler SPDisplaysDataType |grep Resolution

For example

>system_profiler SPDisplaysDataType |grep Resolution
          Resolution: 1920 x 1080 @ 60 Hz

Or to view and change the resolution: Open the Apple menu at the very top-left of the screen and click on System Preferences..., then Displays. This will show a list of available resolutions with the current one highlighted.

Open Terminal app and run this command: system_profiler SPDisplaysDataType. You will see output that looks like this:

$ system_profiler SPDisplaysDataType

Graphics/Displays:

    Intel Iris Graphics 6100:

      Chipset Model: Intel Iris Graphics 6100
      Type: GPU
      Bus: Built-In
      VRAM (Dynamic, Max): 1536 MB
      Vendor: Intel (0x8086)
      Device ID: 0x162b
      Revision ID: 0x0009
      Displays:
        Color LCD:
          Display Type: Retina LCD
          Resolution: 2560 x 1600 Retina
          Retina: Yes
          Pixel Depth: 32-Bit Color (ARGB8888)
          Main Display: Yes
          Mirror: Off
          Online: Yes
          Built-In: Yes