Hi daria1233,
If you are unable to sign in to the App store from your iPhone, and you believe you have changed your Apple ID password in the process, let's try a few things:
Confirm Apple ID and Password
Go to https://appleid.apple.com and see if you are able to sign into your Apple ID account using your Apple ID (which is an email address) and the password you just created. If you are able to log in there, then we know the issue is not with your Apple ID. If you are not able to sign in with the new password, try signing in with the old one. Determine which password works to get you into the website to manage your Apple ID account.
Sign out of the App Store
On your iPhone, go to Settings > iTunes & App Store and click on your Apple ID.
Sign Out of the App Store.
Check Date & Time Settings
On your iPhone, go to Settings > General > Date & Time and confirm or change the Time Zone setting to "Set Automatically"
Reset Network Settings
Do you have your wireless network name and password written down? If so, on your iPhone, go to Settings > General > Reset and choose Reset Network Settings
Restart iPhone & Sign Back in to App Store
Restart your iPhone
Sign back into your iTunes Store account in Settings > iTunes & App Store
Tap on the App Store on your iPhone and see if you can connect to the store.
If this does not resolve your issue, Daria, please reply to this thread with any additional information or error messages you encounter.
Sources:
Manage your Apple ID account information
Sign in with a different Apple ID on your iPhone, iPad, or iPod touch
Get help with the date and time on your iPhone, iPad, and iPod touch
If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network
Restart your iPhone, iPad, or iPod touch
Take care,