The Amateur Radio Band Plan is an important thing to be aware of. Not only are there international band plans, but also National, State and Regional. Check with your local groups for specifics near you. The following content is a general guide and some reference.
From the ARRL
The ARRL provides a high level band plan here: http://www.arrl.org/band-plan. For general operating withing the US most of us keep some sort of visual band plan near by. Below is the ARRL 11X17 PDF Band Plan which you can download from here: http://www.arrl.org/files/file/Regulatory/Band Chart/Band Chart – 11X17 Color.pdf
Band-Chart-11X17-ColorChoose The HF Band That’s Right For You
The text for the description of the following bands is plagiarized from the book “All About Ham Radio” by Harry Helms AA6FW. Copyright © 1992 by High Text Publications, Inc., San Diego, CA, 92121. Library of Congress catalog number: 92-070472. The AA6FW discription just couldn’t be beat!
160 Meters
The band begins just 200 kHz above the upper end of the AM broadcast band, and it is very similar in propagation. Daytime propagation is via ground wave and is generally limited to 100 miles. At night, sky wave propagation takes place over typical distances of a few hundred miles in summer to thousands of miles during the winter. This band offers better sky wave propagation during years of low sunspot activity.
80 Meters
This band has propagation very similar to 160 meters, although sky wave propagation is usually better. Quite a few hams have worked over 100 countries here, and DX contacts of a few thousand miles are common in winter. This band is also better for sky wave propagation during years of low sunspot activity.
40 Meters
This is a transition band with many interesting characteristics. During summer days, it offers reliable communications over 300 miles or so. On winter days, this range can be extended to over 500 miles. Night communications at distances of well over 1000 miles are common, with better conditions during winter frequently allowing intercontinental communications. Unlike 160 and 80 miters, most communications here are via sky wave. The main problem with this band is the interference from powerful international shortwave broadcast stations located outside of North America. If you operate on frequencies without such QRM, however, this is a terrific band for reliable night communications throughout the United States and Canada. Forty meters is better for communications during years of low sunspot activity, although the improvement is not nearly as dramatic as on 160 and 80 meters.
30 Meters
This band is much like 40 meters, although it is limited to CW and RTTY communications and does not suffer interference from international broadcasting stations. This band offers better day and night range than 40 meters, and is an especially good choice for the reliable daytime range out to about 1000 miles or so. This band is usually better at times other than the peak of a sunspot cycle; the increased ionospheric absorption of low frequency signals can reduce the strength of signals on this band.
20 Meters
This is the main band for DXers. During years of low sunspot numbers, there are frequent daytime openings of several thousands of miles. During years of high sunspot activity, the band is often open around the clock to some distant part of the world! During the summer, there are often good evening openings to the west (where the sun is still shining) or to areas to the east where sunrise is taking place. Communications on 20 meters is normally via sky wave, although direct wave communications within a few dozen miles is possible. This holds true for 17, 15, 12, and 10 meters as well.
17 Meters
This band is very similar to 20 meters, although daytime openings are fewer during years of low sunspot numbers.
15 Meters
This band is also much like 20 meters, although it is much more influenced by the sunspot cycle. At the minimum of a sunspot cycle, this band may not open even during the daytime. At the peak, 15 meters is often better than 20 meters for DX communications.
12 Meters
This band is heavily influenced by the sunspot cycle. During years of low sunspot numbers, it is good only for local direct wave communications. During years of high sunspot activity, this band is open d;uring the daytime for DX communications over several thousands of miles. It is also located to the west during the evening hours. When the MUF is just above this band, low powered stations using simple antennas are capable of worldwide communications with ease!
10 Meters
This is like 12 meters, only more so. During years of low sunspot activity, this band is dead for any sort of propagation by the F layer. Communications can be carried on by direct wave over distances of about 25 miles (much like the range of CB radio) and there are often sporadic-E openings of a few hundred miles similar to those found on 50 MHz. When sunspot numbers are high, daytime and early evening DX on 10 meters is spectacular! A very simple, low powered station can easily work over 100 countries that are difficult or impossible to work on 20 meters during a sunspot cycle minimum can be easily worked on 10 meters during a sunspot cycle peak.