I would suggest you get over to this site
And look at the 'Lessons' section for Beginners, as well as some of the articles - specially by Jamey Andreas. I found that place very inspired when I was starting out, with a lot of really good resources for players.
One of the first things to do is relax. A lot of beginners sit forward, put a lot of pressure and effort into their playing, and this slows you down, cramps you up and generally hampers playing.
Sit back, and play one note at a time. Don't rush into songs. See how much pressure it takes to play a note, it's not much. You can pretty much play every note on the fingerboard without using the thumb at all. Just add the thumb for control, not pressure. This will keep you joints more relaxed and help you play for longer, and faster.
Mark Knopfler used to practice chords till he fell asleep - with the guitar in hand. Yes, it dropped to the floor many times, but you don't think of that when you hear him playing. The only way to learn is to practice, but practice correctly. Develop a plan and work on your weak areas. It's the same as preparing for exams or going to a gym.
Don't be worried about playing things fast. Play them correctly, at as slow a speed as is comfortable. Your fingers first have to know what to play. Don't try to keep time with music, or even keep time. Just play it till you're completely familiar with one note, then one chord, then one verse.
Start your excercise routine with a warmup. Chromatic is very good, do this up and down the finger board. Use your four fingers for four frets, and play slowly. Work your way up and down, in forward and reverse order. Later, expand this for alternate patterns and random pattern.
Move then to some scales. Play slowly. Play in doubles, triples and quartets (Two notes, pause, two notes; three notes, pause, three notes....).
Then you can practice some basic chords. Don't worry about rythm, it'll come later.
Move on to a song you know. Do two songs, and don't worry about timing, goin off, or not playing correctly. Just finish the damn thing, and have fun. Try to record yourself, even if on a cellphone, and play it back later. Figure out your mistakes (convert: 'Oh, I'm terrible!' to 'I need to get my timing right' or 'Which chord should I have played then?') and work on them.
Do this for a month and see.
About barre chords, don't worry about making the whole barre. Try just the top four strings (that's all you actually need to make a barre chord) and add variation by barring only the notes you play. And don't put too much hand pressure, you'll just get tired and cramped. If your guitar action is too high, tune down one step or take it to a tech. I am 35 years old, weigh next to nothing, and have no muscle power at all. I can still hold an F barre on a normally set up guitar with .12 strings no problem. It's not the hammer throw.
Most importantly, have fun while playing - that's why you started, right?
Lee Handmade | Takamine EG-240C | Yamaha Classical | Reynolds beater | Tansen electric | RP300 | Marshall MG30RCD | Behringer Eurorack | E-mu1212M | Delta 66 | lots of other crap