You can use blockchain.info and coins.ph as your mobile bitcoin wallets. It is easy to handle all of the transactions and its interface is so smooth and clear with its content. But it will depend on you, Goodluck to you. Wish you choose the best.

You said you're going to buy and sell, using blockchain.info or any online wallet is not recommended for you, even alternative clients like electrum isn't.
Buying at low and selling at high requires a trading platform, without it, you will have to pay fees and wait for confirmation just to do so.

As a newbie you need to use the simplest platform available,
that is Coinbase for USA (and some parts of the world) or Coins for Asian Countries.

For online wallets and wallets that you can download to your smart phone, you can try Blockchain.info and Wallet.btc.com
I tried using both and works for me very well. Blockchain.info and Wallet.btc.com are available for Android users and IOS users.

Buying Bitcoins depends from where you are located, you can buy easily in Coinbase if you are from USA and other countries that they allow selling BTCs. Better look for your community (sub-forum) here if you are not from US and ask around if there's a local exchanger in your area.

Welcome!!

You have a long road ahead of you and I just wanted to give you a good warning.

Be very, very wary of trusting random people from forums on your journey, and careful with links.

I don't want to scare you, but it's similar to 1980 again with all the scammers out there trying to get newbies to the internet.

If you ever need any advice then you can ask me here.

Good luck man and have fun on your journey to the moon.