The apostles determined doctrine and how they made sure that everyone was teaching the same doctrine once it had been revealed. It also shows that a single apostle did not consider himself able to establish doctrine.  

Note how the spiritual gifts in apostles gave the final answer. Then, the doctrine was entrusted to faithful men and carried to the local elders who must be apt to teach--the must be able to cause the people to understand the doctrine:  

Acts 15:1-31 "And certain men which came down from Judaea taught the brethren, and said, Except ye be circumcised after the manner of Moses, ye cannot be saved. When therefore Paul and Barnabas had no small dissension and disputation with them, they determined that Paul and Barnabas, and certain other of them, should go up to Jerusalem to the apostles and elders about this question. And being brought on their way by the church, they passed through Phenice and Samaria, declaring the conversion of the Gentiles: and they caused great joy to all the brethren. And when they were come to Jerusalem, they were received of the church, and of the apostles and elders, and they declared all things that God had done with them. But there rose up certain of the sect of the Pharisees which believed, saying, That it was needful to circumcise them, and to command them to keep the law of Moses. And the apostles and elders came together for to consider of this matter. And when there had been much disputing, Peter rose up, and said to them, Men and brethren, ye know how that a good while ago God made choice among us, that the Gentiles by my mouth should hear the word of the gospel, and believe. And God, which knoweth the hearts, bare them witness, giving them the Holy Ghost, even as he did to us; And put no difference between us and them, purifying their hearts by faith. Now therefore why tempt ye God, to put a yoke upon the neck of the disciples, which neither our fathers nor we were able to bear? But we believe that through the grace of the Lord Jesus Christ we shall be saved, even as they. Then all the multitude kept silence, and gave audience to Barnabas and Paul, declaring what miracles and wonders God had wrought among the Gentiles by them. And after they had held their peace, James answered, saying, Men and brethren, hearken to me: Simeon hath declared how God at the first did visit the Gentiles, to take out of them a people for his name. And to this agree the words of the prophets; as it is written, After this I will return, and will build again the tabernacle of David, which is fallen down; and I will build again the ruins thereof, and I will set it up: That the residue of men might seek after the Lord, and all the Gentiles, upon whom my name is called, saith the Lord, who doeth all these things. Known to God are all his works from the beginning of the world. Wherefore my sentence is, that we trouble not them, which from among the Gentiles are turned to God: But that we write to them, that they abstain from pollutions of idols, and from fornication, and from things strangled, and from blood. For Moses of old time hath in every city them that preach him, being read in the synagogues every sabbath day. Then pleased it the apostles and elders, with the whole church, to send chosen men of their own company to Antioch with Paul and Barnabas; namely, Judas surnamed Barsabas, and Silas, chief men among the brethren: And they wrote letters by them after this manner; The apostles and elders and brethren send greeting to the brethren which are of the Gentiles in Antioch and Syria and Cilicia: Forasmuch as we have heard, that certain which went out from us have troubled you with words, subverting your souls, saying, Ye must be circumcised, and keep the law: to whom we gave no such commandment: It seemed good to us, being assembled with one accord, to send chosen men to you with our beloved Barnabas and Paul, Men that have hazarded their lives for the name of our Lord Jesus Christ. We have sent therefore Judas and Silas, who shall also tell you the same things by mouth. For it seemed good to the Holy Ghost, and to us, to lay upon you no greater burden than these necessary things; That ye abstain from meats offered to idols, and from blood, and from things strangled, and from fornication: from which if ye keep yourselves, ye shall do well. Fare ye well. So when they were dismissed, they came to Antioch: and when they had gathered the multitude together, they delivered the epistle: Which when they had read, they rejoiced for the consolation."

Let God be true and every man a liar.

Apostles are given the responsibility of protecting the entire flock of God from the attack of the enemy, but with so many voices in the world, each one claiming to be the one that should be listened to, how can you know?  You are responsible to be close enough to God so that you can tell the difference between false apostles and real apostles.

Read the complete definition of "Apostle."