Which it teaches by enabling us to (1) originally recognize which writings were cannonical scripture and (2) giving us the ability to understand scripture. The Church is nothing more the the "called out" - the collection of all regenerated Christians, ie. those fileed with and directed by the Spirit. Now, just as the Pharisees perverted the concept of Israel with their man made traditions (as condemned by Jesus) so have false Christians created a false and perverted "Church' with their traditions. For pretty much the same reasons. This is the reason for Sola Scirpture and why Christ relied on scripture. He recognized that slavish obedience to non-scriptural traditions would always lead man away from God. ("You praiase me with your lips but your heart is far from me, you have traded the commands of God for the precepts of man"). Paul spoke from direct relevation of Christ - just as the prophets spoke, and even he used scripture as authority for many of his arguments but never tradition. Nor is it tradition, but the Spirit, which defines the cannon. It was this cannon which shaped the corporate nature of the Church not the other way around. To reject Sola Scriputra is to fall into idolatry every time. Every body that has placed tradition on the same level as scripture has fallen into apostasy just as the scribes and pharisees did. It is inevitable. Tradition is just the reign of the flesh.
Who's "us"? Historically, it was the church -- the one that started at Pentecost and had priests, bishops, and yes -- Popes -- which recognized the canonicity of Scripture.
(Incidentally, that right there destroys sola Scriptura, because the Scriptura by itself is not sufficient to give you its own table of contents.)
And "giving us the ability to understand scripture"? Understand it exactly how? The way the LCMS Lutherans understand it? The way Southern Baptists understand it? The way the Assembly of God understands it? The Holy Spirit cannot be the author of contradiction; I hope you would agree with that.