How to do an Apple ID and how to download in iphoneSE

You have an Apple ID. You used it to sign into the Support Community. See the article below that covers how to set up a new phone.

Set up your iPhone, iPad, or iPod touch

To download apps, use the App Store. Use iTunes to purchase music.

See Change your Apple ID https://support.apple.com/en-us/HT202667. 

And see What to do after you change your Apple ID or Password https://support.apple.com/en-us/HT204071 (supplementary to what the fist link says) 

Post back if you have questions about what you can do if your Apple ID (1) is a third-party apple ID or (2) ends in icloud.com, me.com, or mac.com. 

And FYI, see iCloud: About your @icloud.com, @me.com, and @mac.com email addresses https://support.apple.com/en-us/HT201771

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You also can use What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch https://support.apple.com/en-us/HT201351

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Note that neither will work if someone else's Apple ID is shown on your phone. In this case, see Turn off Activation Lock https://support.apple.com/en-us/HT20144, and then post back.