now using Mac OS high Sierra 10.13.6. I can not download apps in App Store. can I upgrade to macOS Catalina ? I required 10.15 person to download apps. what should I do now ?

High Sierra 10.13.6 is the highest possible upgrade for a 2010 MacBook Pro.

Also see the following from Identify your MacBook Pro model - Apple Support

MacBook Pro (17-inch, Mid 2010)

Model Identifier: MacBookPro6,1

Part Number: MC024xx/A

Newest compatible operating system: macOS High Sierra 10.13.6

Tech Specs: MacBook Pro (17-inch, Mid 2010)

MacBook Pro (15-inch, Mid 2010)

Model Identifier: MacBookPro6,2

Part Numbers: MC373xx/A, MC372xx/A, MC371xx/A

Newest compatible operating system: macOS High Sierra 10.13.6

Tech Specs: MacBook Pro (15-inch, Mid 2010)

MacBook Pro (13-inch, Mid 2010)

Model Identifier: MacBookPro7,1

Part Numbers: MC375xx/A, MC374xx/A

Newest compatible operating system: macOS High Sierra 10.13.6

Tech Specs: MacBook Pro (13-inch, Mid 2010)