The '58 is a close-proximity cardioid stage mic used primarily for vocals. They're built tough to take knocks, and while they deliver good sound, their biggest asset is that they take a lot of knocking around. If you intend doing a lot of picking, I'd recommend a more studio-based mic, mainly because the '58 rolls off frequencies above 15kHz... and the higher harmonics of your guitar might sound a little dead.
I just thought I'd throw that at you, in case you're placing the mic more than a hand-span away from your source instrument, be it your mouth or your strings
If you are trying to record BOTH your guitar and your vocals at the same time with one '58... Uh, I'd advise either recording the guitar track and the vocal track separately, or buying another mic.
It's rare that any microphone can connect straight to a comp without some sort of pre-amplification. Mic signals are pretty quiet - They have to be, as the pick-up arrangement involves distances of less than the thickness of paper, and high voltages just arc across these distances, totally ruining your day.
Pre-amps come in different arrangements. They can be simply a hard-wired black box with an ON switch and an attenuation knob. They can be a 24-channel mixing desk with attenuation, EQ, effects busses, faders, pan knobs and lots of other toys. But the basic principle is still there - take a very weak signal, amplify it, pass it on to the master input device.
Currently, your microphone's input signal is too quiet for GB's in-built volume sliders to handle - All they can do is amplify what's already there, rather than boost the mic signal before you record it. Pre-amps are not included with computer hardware because there are several electrical 'standards' that are used in the audio signal world that use the same plugs... And if you plug the wrong cable into a perfectly fitting hole FWAP!!! Mac-burger.
Good news: There's no such thing as 'best'. What matters are the choices you make with each song/ piece/ arrangement. Each guitar has peculiar tonal qualities, as do voices - You're own experimentation will reveal each instrument's qualities.
Single mic placement for a guitar TENDS to average out at about the 12-15th fret. This is not a rule, it's just where most people start. Listen for intrusions: things like too much plectrum noise, booming on certain notes, fret noise, finger noise, your rings hitting the sound board. In some pieces you will WANT to emphasize an 'earthier', fingered sound to your guitar, so consider finger-noise as a set of options, rather than things you must get rid of.
In a two-mic set up, you need to be comfortable, and the mics need to accomodate your posture. Never sacrifice the way you feel comfortable playing to the limitations of your seating or your mic stands, unless you want to be billed as the Musical Hunchback. It might be that you can 'pick up' an acoustic guitar pickup - these specialised mics can be clipped into your guitar's sound hole, are fairly cheap, and while this can create certain mic position limitations, they're damned convenient.
With regard to effects... Snakes alive, there's so much digital stuff you can cast on a signal these days it's neither a science nor an art, it's evil black magic mumbo-jumbo. But possibly the most important is Equalisation, or EQ.
Depending on your mic placement and the acoustics of the environment you're playing in, certain frequencies might be unwanted - The low frequency booming of your bottom E, or for some reason when you strum a certain chord, the volume shoots way up and distorts your recording. Enter EQ. Ideally, you'd make several recordings with different EQ settings until you hit a combination that fits well with the rest of the piece. Then you'd save that combo for use later.
Unless you're after some pretty distressed sounds, use EQ to tailor the source sound. Try not to use it to make up for 'lost' information - For instance, because your '58 won't record sounds over 15kHz, there might be a temptation to 'boost' the higher frequencies to make the recording sound crisp. While there will be some success here, you will also be boosting signal hiss that accompanies the recording. In some cases, you may be trying to boost frequencies that simply weren't recorded. USe EQ sparingly and intelligently, and you'll treat your composition well.
Good luck with your recordings. Get a pre-amp.
-Oro
