The key signature at the start of a line of printed music announces both what sharps or flats are being used in the song, as well as what key the song is in. If there is just one flat in the key signature, the flat is always Bb. Two flats in the key signature are always Bb and Eb. 3 flats in the key signature would be Bb, Eb, and Ab. 4 flats would be Bb, Eb, Ab, and Db. Then comes Gb, Cb, and Fb. You can easily remember the order of the flats by spelling the word “BEAD” and then recall the phrase “Go Catch Fish.”
The sharps in a key signature are just reverse from the flats; instead of BEADGCF, the order of the sharps is FCGDAEB. So one sharp in the key signature is F#, 2 sharps in the key signature would be F# and C#, and so on.

The circle of 5th (or circle of keys) shows the relationship between the various keys one can play in, and each subsequent key is a 5th away from the previous key (or a 4th away — depends on which way you move in the circle). For example, the key of C has no sharps or flats. To the right of the key of C on the circle is the key of F with one flat, while to the left of the key of C on the circle is the key of G. Each subsequent key has one more flat in the key signature (as you move to the right) or one more sharp (as you move to the left.) Watch the short video:

< For more information on the circle, please go to http://www.playpiano.com/101-tips/20-circle-of-keys.htm

Complex 2-hand voicing for piano is done in various ways, but this video shows one way to do it using a simple chord progression. Watch the voicing develop as we move from simple triads to 7ths to octave-5ths in the right hand to 13ths and 9ths along with the 7th in the left hand, while the damper pedal sustains a low root on the first chord of the progression:

Every major scale has a “kissing cousin” which is related to it known as a “relative minor scale”. It is related because it uses the same notes as the relative major scale in its natural form.
There are three types of minor scales: natural minor, harmonic minor, and melodic minor. Watch this 8-minute video:

The key of Bb major has two flats in the key signature — Bb and Eb. The primary chords are Bb, Eb, and F, and the main secondary chords are Cm, Dm and Gm. Watch this short video:

An inversion in music is a chord or interval which is “upside down.” For example, if you invert an interval of a 3rd, you get an interval of a 6th. If you invert a C chord in root position, for example, you turn it on it’s head so that C is no longer on the bottom, but now is either the middle or the top note of the chord. For more information on inversions, please go to http://www.playpiano.com/101-tips/5-inversions.htm

All musicians of any kind can benefit from developing his or her ear. Some people are born with a better ear than others, of course, but those of us who don’t have a great natural ear can still improve a lot through the use of ear-training drills.
One drill that is useful is to have a friend or relative play various intervals on the keyboard — start with 2nds, then 3rds, then 4ths, 5ths, 6ths, 7ths, etc. — and see if you can identify them. By doing this just a few minutes a day most people can improve their musical ear signaficantly.
Another drill is to have someone play chords of various sorts on the keyboard, and see if you can identify them . Start with the easy ones like major and minor, and gradually work up to augmented and diminished chords, then 6ths and minor 6th chords, and so on. If you don’t have a teacher or someone to help you, you can take online courses in ear-training such as the ones at http://www.playpianocatalog.com/eartrco.html

Here’s a 5-minute video on a useful chord substitution technique where you “slide into” the next chord in a song from 1/2 step above or 1/2 step below: