The context of something is what surrounds it. Context of scripture is the scripture that is found before and after the specific text that you may be studying. Context can reveal much about the meaning of scripture.
For instance, many people take the following portion of scripture out of context. This is the day which the LORD hath made; we will rejoice and be glad in it. - Psalm 118:24 They think that this means today, this beautiful day that we now walk and breath in. However, if you read verses 17 to 23 along with it, you find out that the day that this is speaking of, is the day that Jesus died on the cross.
Another example of misunderstanding which comes from not considering the context is the verse, For where two or three are gathered together in my name, there am I in the midst of them. - Matthew 18:20 Much of the time, this verse is quoted to and assumed to say that God is here with us in this church meeting. While it is true that God is with believers when they meet, this verse not talking about that. If you read verses 15 to 19 along with verse 20, you will find that the context is church discipline. If someone in the church is living in sin and refuses to give it up, the church is to discipline that person, and this verse is saying that God is behind the church in this matter.
Scripture must also be understood in the context of the whole Bible. For instance, if you read a portion of scripture that seems to contradict other parts of the Bible, you probably do not understand that scripture properly, or you may not understand the other scriptures that it seems to be contradicting. Pray that God would give you proper understanding and that He would lead you into all truth for His glory.