Hey, another Windows Phone user! There aren't a lot of us...
All apps are available from the Store, represented on your Home screen by an icon that looks like a shopping bag with a handle.
NOTE: If in doubt about anything, click the row of three dots. This will expand those cryptic icons and tell you what those icons are supposed to do, plus you often get more menu choices.
You absolutely MUST get two particular apps, both from Microsoft.
1) Files (yes, that's the exact name of the app! Accept no imitators!)
This allows you to browse your phone as though it were a computer, which you cannot do unless you have this app installed.
2) Contacts + Message Backup (exact name, again)
This is new, and is a belated response by MS to a storm of complaints about the previous inability to copy your data to a location other than "the cloud". This app backs-up your contacts and messages to your SD card (if you have one...). Not the best solution, but the best that MS allows you at the moment.
For Weather, get The Weather Channel app. You can set multiple "locations" to keep track of, and you can easily slide the screen from one to the other. Works well.
I also have the Simply Advanced Unit Converter for converting between standard and Metric measures.
All of these are free.
I also strongly urge you to set a password on your phone, even if it's just "1234". Setting a password keeps the phone from "pocket dialing", which it WILL do -- embarrassingly -- unless you set a password.
What other interests do you have?