Dear Crystal:
I praise God that you are considering joining the true church of Jesus Christ, the Catholic Church. We will be praying for you as you make this very important decision.
As a new Catholic it will be very important for you to focus on learning about the Catholic faith. In that context it is best that you not watch sermons on TV or go to a friend's church as this may confuse you. Much of what the Protestants believe is the same as Catholics believe, but there are also some very important differences. Until you are secure in the knowledge of your Catholic faith it would not be wise to listen to, read materials from, or attend non-Catholic churches.
This is not a mandate, but it is what is prudent to be sure that your Catholic faith, which you are just now learning, is allowed to grow and mature without any contamination from non-Catholic ideas.
Once you are secure in the knowledge of your Catholic faith you will be able to watch those sermons on TV and not become confused, or visit the churches of your friends without becoming confused.
What the Catholic Church does require, is that you must attend Sunday Mass or the Saturday vigil Mass. You can never choose to go to a non-Catholic service instead of going to a Catholic Mass. You may visit the non-Catholic church of a friend on Sunday morning only if you have been to the Saturday vigil Mass or Sunday Mass. To miss the Sunday liturgy without valid excuse (i.e., illness, infirmity, or other reason that, through no fault of your own, you cannot make it to Mass) is a grave sin.
Thus, if you do decide to visit a friend's non-Catholic church just be sure that doing so does not cause you to miss celebrating the Catholic Mass for that Sunday.
I would suggest, however, that attendance at a non-Catholic church should be relatively rare. You'll be Catholic and thus you need to focus on your Catholic faith. But there is nothing wrong with visiting a non-Catholic church as long as you do not neglect attending Sunday Mass.
There is nothing wrong with having non-Catholic friends. In fact, it is possible that being friends with non-Catholics can give those non-Catholics a perspective on the Catholic Church that they did not have before. Many non-Catholics have negative and erroneous ideas about the Catholic Church. Friendship with those non-Catholics may help them to understand the true nature and teachings of the Church.
With that said, be sure you are not influenced or confused by their non-Catholic ideas. Always guard your faith. Do not do anything jeopardize your faith. Faith is a precious thing. Coming into the fullness of the faith, which is the Catholic Church, is more precious than gold.
Jesus is waiting for you, Crystal. He is waiting to embrace you into the fullness of his Church, the Church that he personally founded. Once you are received into the Catholic Church and are able to partake of our Lord in the Eucharist it will be an experience that is almost too much to put into words.
May God bless you, may our holy Blessed Mother guide you, and may St. Michael the Archangel protect you as you begin your journey to Christ's Church.
God Bless,
Bro. Ignatius Mary