空白PHP屏幕 - 使用表单更新数据库

I'm pretty new to this so please bear with me. I'm trying to make a page where a logged in user can update their row of information in the database. I've been sitting here for hours trying to figure this out, so maybe someone can help shed some light on this. Right now I'm even getting a blank white page and can't figure out why.I'm pretty new to this so please bear with me.