Thanks for your question.
Ye we believe that there is only one God. Contrary to the false doctrine of the Trinity, the Bible teaches that God is unique and that Jesus was and still is a human being and that the Holy Spirit is God's power and not a separate personality. The doctrine of the Trinity comes from pagan sources and not from the Bible.
Here is some information on the website which you will find useful in answering this question more fully:
If you want to come to grips with what the Bible really teaches, why not take the free study course available on https://www.thisisyourbible.com? You may take the course online or by regular mail and proceed at your own pace.
This course will give you a background in the major themes of the Bible from Genesis to Revelation. As with everything we offer, there is no cost to you other than your time and effort. You will also have a personal tutor to whom you may pose questions either from the course itself or those questions which come to you as you read the Bible.
I hope you have found this helpful.
God bless and keep you!