Next to the Bible, God guides us through circumstances. We read Scripture because it contains His principles to direct our decisions. We also read His providence through circumstances which He sovereignly controls. By way of the circumstances He shows, God reveals His individual will to our lives.
"Open doors, closed doors" is one signpost for discerning God's guidance through circumstances. It's a common way for God to indicate "Yes, this is My will for you" or "No, this is not My will for you." If you apply for visa to the United States, and the embassy turned you down several times, you should probably see that God is saying "No" to you on the plan. It's possible He's the one closing the doors.
But God always works for the good of His children. When He closes doors, He always has something better behind another door. God also leads by opening doors for us. Paul's example reminds us of this when he regularly prayed for God to open doors for him (Colossians 4:3). At one time, he was directed to stay in Ephesus by an open door (1 Corinthians 16).
A call for spiritual discernment applies here though. Sometimes a door may "look closed" to you, but God may just be testing you. God may be ready to open the door sooner or later. However, He is using the closed door to prepare and strengthen your faith. In such a case, God is simply saying "Wait!" to you.
I am happiest when doors are open. For some periods of my life, however, doors are closed. Days, weeks, months pass. Then I begin to struggle. I forget that God is telling something to me. Is God saying "Yes," "No," or "Wait?" At times like this, uncertainty or fears must be fought with all the weapons of God's spiritual arsenal so I'd know what to do next.
In reading God's circumstantial guidance, believers are not left unaided. A Christian has the assurance that the Holy Spirit aids him in understanding Scripture. He is also assured that the Holy Spirit will aid him in understanding God's providence through circumstances. The Bible says the Holy Spirit is the believer's Guide (John 16:13).