But can you sight read (from tab) a song you've never heard before?

Playing with the song being played for the most part yes.

The only advantage sheet music has is the addition of time values but you can do that with more professional tabs, so in essence yes i could do that if the tab were accurate enough to include the timing.

Also sight reading doesn't completely revolve around pieces you've never heard before. Most of the time when people sight read sheet music its because they've heard it before but don't have allthe notes memorized. So i really don't see it surprising especially since tabs literally tell you where your fingers go, where as sheet music gives you the note it must be played on so which fret you use for that value is totally up to you.

That's a good point. That's one of the things that confused me reading a regular score. Practice would be great help.

so if the time sig is 4,4 does that mean ther will be4 whole notes (or 8 half etc.)in the whole measure?

No, there would be 4 quarter notes, 2 half notes, 1 whole note. Say you have a time signature x/y, x refers to the number of beats per measure, and y refers to the type of note that gets one beat (2 for half note, 4 for quarter, 8 for eighth, etc..) For example, in common 4/4 time:


So in 4/4, a quarter note gets one beat, half gets two, and whole gets 4. Also, a eighth gets half a beat, a sixteenth gets a 1/4 a beat, and so on. If you look at something more complicated like 12/8, you have 12 beats to a measure and an eighth note gets one beat. So then a sixteenth note gets half a beat, a quarter note gets two beats, a half gets four, a whole gets eight. Hopefully that clears it up.

Well im trying to tab a song and know were to put the bar lines
Is that right?
All that is 4 wholnotes (equivelent in length)

so on 4,4 would i put the barline after each wholenote (or equivilent)

The song is All Dark Graves by the Faceless btw.

well the notes and nad numbers arent lineing up even

If I've understood your tab right, here's how I think it should lay out in 4/4 time.
I've shown a line of dots beneath to mark the beats.
This is assuming, by the way, that your first note (dotted half-note) falls on beat one of the bar - which it looks like it should.
Your last bar is incomplete, because a half note and two 8ths only make 3 beats. "(X)" marks the missing quarter note space. So either you need another quarter note, or a quarter note rest, or you need to make the last note a dotted quarter.
(It's just possible you have a 3/4 bar, but that would only apply if a downbeat fell immediately after that last 8th note, right on the (X). It would feel like a break in the rhythm, a missing beat - not a gap in the rhythm, a 1-beat rest, but a kind of stumbling rhythm. This is pretty unusual in rock, but can occur.)

In notation, you don't need to space notes exactly according to their value (bars with few notes can take less space than bars with lots of notes), but it's obviously clearest if you give long notes more space than short ones; think of a bar divided into 4 beats, and just place the notes roughly where they would occur in time.
Check out some published notation for a guide to what looks right.

Just figure out which lines and spaces correspond to which notes, and take it little by little. There's no real way to teach it other than by practice. Since you're playing viola, and (I presume) using alto or tenor clef, I can't tell you which are which, as I play the piano and use only treble and bass clefs, but I would certainly think that you could find that part online. :)

I find that you really finally learn how to read music when you finally can easily write/notate it. I've been using this book for like 10 years to help me keep my music reading/writing chops up.

The first step in understanding rhythms is to memorize the various notes and their 'values.' You don't need to understand them now, but for information's sake, look over the five most commonly used notes:

It's confusing to think of something being an eighth of a beat, and you may wonder why a note that is one beat long is called a quarter note. Why wouldn't it be called a whole note, since it's a whole beat?

It's because we name our notes based on the length of time they are played within a measure, not based on how many beats they are.

I often tell my students to think of a measure as a whole pie, in that it can be cut into quarters (4 pieces), eighths (8 pieces), and so on. A whole note is called a whole note because it is played and held for a whole measure. A quarter note is called a quarter note because a full quarter note takes up exactly one quarter of a measure.

I know what you're saying. "Yuck! Fractions!" To this, I hang my head sadly and nod. You're absolutely right. But I'm not going to make you add fractions, or anything like that. If you get the pie illustration, then you're set.

Now that we understand why the notes are named the way they are, let's look at the chart again:

Dividing a measure up into eighths and sixteenths on the fly while playing would be difficult, especially with complicated rhythms, so this is useful mostly as an understanding of the basics. The next step to take is to actually count through the rhythms.

how to read sheet music
 

usually there are guitar tabs on sheet music too