The passport owner is given permission to enter the country for a limited time. In most cases it's a month or 90 days. When applying for a visa you must send your passport to the embassy. The actual turnaround time can vary from a few days to a few weeks and usually comes with a handling fee in the range of 50-300 Dollars.
If you are traveling to several countries that require a visa, it can be a bureaucratic dance on a tightrope to get all visas into your passport before setting out on your backpacker trip.
Some countries does not allow you to apply for a visa more than 6 months in advance. If you are setting out on a backpacker trip for 6-12 months, this may cause a few problems, since you need your passport at all times while traveling. You travel consultant at KILROY can advise you on how to proceed with visa applications and in some cases helps you to get all visas aboard.