There are tons of ways to buy bitcoins these days if you search in google instead of here. Many of them i personally used and the best which i can recommend is Coinbase and Localbitcoins .
And as you mentioned that you are looking to buy bitcoin with cash only then i will highly suggest you to go with localbitcoins because there are tons of people offering bitcoins for cash near you probably. But as compare to any other online transfer method i noticed that seller on localbitcoin who sells via cash wil charge some more high rates . Good Luck for your buyings.