How to become a muslim:
If you believe in a one and only God, that you beleive that Mohammed is his last messenger then you are already holding the beliefs of a Muslim.
All you need to do to make that official, is recite the following prayer inshallah:
أشهد أن لا إله إلا الله وأشهد أن محمد رسول الله
Ash-hadu alla ilaha illallah-wa ash-hadu anna Muhammadan abduhu wa rasulullah
"I bear witness that there is no God except Allah and Muhammad (SAW) is His messenger".
Once you have recited that with the meaning of it in your heart, you can call yourself a Muslim.
Anyone can become a Muslim, there are no rules whatsoever: if you have tatooes you can still become Muslim, if you were from any other religion, you can become muslim, wither you are male, female, single, married, engaged, a child, a teen or in your later years, you can become a Muslim.
You can take your Shahada at home, in private, in front of some muslim friends as witnesses or at the mosque with an Imam inshallah.
You do not need to take a course, or pay for a certificate to become Muslim. However, you will need a certificate for when you go to Hajj, the holy pilgrimage.
Once you have taken your Shahada, it is important to have a shower, sort of like to wash away your past sins. You can do a Gusul if you know how to, but cleaning yourself with running clear water is the most important part of this step.
A beautiful journey lies ahead of you, Inshallah. It won't be easy or all smooth,but Allah will give you the strength you need and you will feel happier than ever, Inshallah.
Start learning your prayers, how to do your wudu, learn about ramaddan and start reading the Qu'ran for guidance. The Holy Book is your only sure source of information. Make sure you reffer to the books before you listen to other people.
They are many books and websites that will teach you in details what you need.
Here is a good link: http://www.wikihow.com/Become-a-Muslim
If you are based in London or near London, Turning Point Academy teaches new sisters the basics of islam, from shahada to recitation of the Qu'ran! It is open to any non-muslim or revert whishing to learn about Islam, Mashallah.
(COMING SOON: HOW TO DO WUDU)