Hi there srinivas121,
It sounds as though when opening an application you're seeing that it first needs to be installed before it can be used. You're in the right place to seek a solution and, I'd be happy to assist.
Below is a resource that can help:
How to check the storage on your iPhone, iPad, and iPod touch
It sounds as though the "Offload Unused Apps" feature may be enabled which can uninstall apps when storage is low. On your iPhone, tap Settings > General > [Device] Storage. Do you seeing a "Storage Almost Full" alert?
Have a great day!