Generally, guesting is in header.

I cannot understand how to use GetActiveUniform function.

public void GetActiveUniform(uint program, 
                             uint index, 
                             int bufSize, 
                             int[] length, 
                             int[] size, 
                             uint[] type, 
                             string name);

My attempt looks like this (everything is compiled and linked):

        var uniformSize = new int[1];
        var unifromLength = new int[1];
        var uniformType = new uint[1];
        var uniformName = "";
        Gl.GetActiveUniform(Id, index, uniformNameMaxLength[0], unifromLength, uniformSize, uniformType, uniformName);

After call I get proper uniformSize, length and type, but not name.