There are many factors when it comes to development, but I would consider the big three to be:
1. Security
2. Performance
3. Maintainability
A framework often provides you with a pretty good foundation having those three in mind. It also forces you to think and learn about best practices like coding syntax, programming patterns, testability, localization, authentication, and more.
On top of that, if you're starting out learning a new language, the code you "write" is initially pieced together by examples and tutorials on how to solve isolated problems, but that doesn't help with having an overarching and cohesive application in the end. In addition, the examples you find online may not follow best practices and may not even teach you the right thing.
Two frameworks I would suggest you look into are:
1. Yii - A proven and sustainable framework that really takes the big three to heart
2. Laravel - A newcomer that has gained a lot of traction for its easy of use and intuitive feel
Both would be good choices for most projects. Seeing as you're just starting out, it would be very difficult to research the best possible framework for your particular project, so considering you have to start somewhere to learn so that you're later able to compare, both of those frameworks mentioned would be a good place to start.
~Sovereign