Tubes: the basics.

There are 3 general categories of enteral tubes (tubes that go into the enteric, or digestive system).

1) NG tube, or Naso-Gastric tube. 
It goes up through a nostril and down the esophagus into the stomach.  It is usually secured just by a bit of tape on the face.  There is also a variant on this called an NJ tube (Naso-jejunal tube) that extends beyond and through the stomach to the jejunem, a part of the upper intestines (see j-tube below for more on this).

NG tubes are generally short-term things.  If someone is going to need intubation for a long period then usually one of the below options will take its place.  I've had an NG tube and can confidently assert that from a patient point of view they fully suck.  I had mine for maybe a week and it always hurt at the back of my throat, was even worse when I swallowed, and created both callus and tender tissue there.  It feels invasive and obstructive.  Still, they're a very necessary thing in some situations.  They are generally a smaller diameter than g-tubes or j-tubes, but you can feed through them.  Blenderized foods typically have to be a bit thinner in consistency due to this smaller diameter.

2)  G-Tube, or Gastrostomy tube (also called PEG tube for Percutaneous Endoscopic Gastrostomy).
These go from the outside of the body through a hole or stoma in the abdomen directly into the stomach.  There are many variations on this, with long flexible tubes and small low-profile 'buttons'.  It is the main form of feeding tube used, and the majority of people seem to tolerate them quite well once they're used to it.  I have one, and I suppose am understandably fond of it because my alternative would be starvation. Feeding may be with commercially available formulas or blenderized foods.

G-tubes are placed often just under sedation using an endoscope (hence the 'E' in PEG) but sometimes using general aeaesthetic, especially if other surgery is required.  They are secured on the outside with some variety of disk or bumper that prevents the tube slipping inwards and on the inside by a water-filled balloon or collapsible obturator (sort of mushroom-shaped usually) to stop it falling out.  Depending on type,care, and luck, g-tubes need changing at different frequencies.  The shortest change interval I've seen from a manufacturer is 3 months, but in reality I know that many people have to change some types of devices as often as every few weeks.  Balloon types can in most cases easily be changed at home with no anaesthetic or drama.  On the other hand, some types of g-tube can last 2 or even 3 years before having to be changed.  Obturator types need some medical intervention to change, but it's a very minor procedure, with no sedation etc required.

Feeding is done either by using a syringe (called bolus feeding) or a special pump.

You'll find lots of blog posts and articles written on g-tubes and issues around them.  There is also a variant called a g-j tube.  See j-tube below for more.

3) J-Tube. The "J" is for Jejunostomy.
There are many reasons for needing to place a tube further down someone's digestive tract, and a j-tube does this.  It can be percutaneous, coming directly from the outside like a g-tube, or more commonly as a g-j tube, where a g-tube placement is done with a j-tube running through inside the g-tube into the intestine.  Some people have separate g- and j- sites.  Typically special formulas are used when feeding with a j-tube, called 'elemental' formulas.  These are partly digested as of course apart from the mouth digestion being missed the stomach digestion is too.  I am aware however of some adults at least adapting to certain real foods in a blenderized diet for j-tube feeding.  The body is an amazing and infinitely variable thing, yes?  most usually feeding is done with a pump for j-tubes.

These are the very barest basics only.  See the LINKS page for other resources, and if you find one elsewhere you think could be useful, please let me know.  You'll also find blog posts and articles on all things tubey.