G'day, i have just started playing again after about a 5 year break about 6 months ago. Its all coming back to me pretty well but i have some questions about tabs i find a lot of chords that have a dash in the middle example F/G i can only assume it means go from F maj to a G maj quickly? am i right. and also i often find a tab number with brackets around it so (3) meaning 3rd fret whatever string what does the brackets mean.
F/G - called a "slash" chord, and the first letter represents the typical chord, the second letter represents the bass note. In this case you would fret E @ 3rd instead of 1st. similarily D/F is a pretty prominent one you may come across in a lot of songs. Its just a std D with the addition of E @ 2nd fret. should be charts and what not online if you want to dig deeper. As i understand it just about any chord can become a slash chord by changing the bass note.

the brackets can mean a few things. Generally its a "Ghost" note, wherein you let that note ring as you continue. Some ppl say its an optional note. Its also used to denote harmonics (ie; (7), (12), etc.. ). In the case of (3) probably harmonic, but listen to the song to figure it out. if its harmonic should be somewhat apparent in the song. Sometimes has N.H above it (Natural harmonic). You may already know this, but these are played by resting your finger (NOT FRETTING) just over the string (barely touching and over the fret bar, not in the middle of the fret) and picking the note. Its easier at e,B,G, (12) if your playing around and trying to learn them, but essentially works on all 6 strings. N.H can be found at 3rd, 5th, 7th & 12th frets. 5 and 3 are harder to pull off on acoustic, but work well on electric.
i'm gonna have to read what you wrote about 10 times to even kinda understand it if you can explain it simpler ( about the F/G thing) plese do it sounds like you know what your talking about. if not can you advise where i can find a chord chart with these added notes. Thanks for the imput guys!!