Pick a Subject.Talk to your Scoutmaster about your interests. Read the requirements ofthe merit badges you think might interest you. Pick one to earn. YourScoutmaster will give you the name of a person from a list of approved merit badge counselors (MBC). These counselors have special knowledge in their meritbadge subjects and are interested in helping you.

Scout Buddy System. You must have another person with you at each meeting with the merit badge counselor. This person can be another Scout, your parents or guardian, a brother or sister or other relative, or a friend. It is acceptable to meet with the MBC in a public place, such as a cafe or library. It is NEVER acceptable to meet with an MBC (or any other Scouter) alone (one on one). See Youth Protection.

Call the Counselor.Get a signed merit badge application from your Scoutmaster. Get intouch with the MBC and tell him or her that you wantto earn the merit badge. The counselor may ask to meet you to explainwhat is expected of you and to start helping you meet the requirements.You should also discuss work that you have already started or possiblycompleted.

Unless otherwise specified, work for a requirement can be started at any time.Ask your counselor to help you learn the things you need to know or do.You should read the merit badge pamphlet on the subject. Many troops and school or public libraries have them. (See the BSA publication numbered list here.)

Show Your Stuff.When you are ready, call the MBC again to make an appointment to meet the requirements. When you go take along the things you have made to meet the requirements. If they are too big to move, take pictures or have an adult tell in writing what you have done. The counselor will ask you to do each requirement to make sure that you know your stuff and have done or can do the things required.

Get the Badge.When the counselor is satisfied that you have met each requirement, he or she will sign your application. Give the signed application to your Scoutmaster so that your merit badge emblem can be secured for you.

Requirements.You are expected to meet the requirements as they are stated—no more and no less. You are expected to do exactly what is stated in the requirements. If it says "show or demonstrate," that is what you must do. Just telling about it isn't enough. The same thing holds true for such words as "make," "list," "in the field," and "collect, identify, and label." 

The requirements listed here are the official requirements of the Boy Scouts of America, taken directly from their website. However, these requirements  might not match those in the Boy Scout Handbook and the merit badge pamphlets, because this publication is updated only on an annual basis.

If a Scout has already started working on a merit badge when a new edition of the pamphlet is introduced, he should continue to use the same merit badge pamphlet and fulfill the requirements therein to earn the badge. He need not start all over again with the new pamphlet and possibly revised requirements.

The above from Scouting.org "Introduction to Merit Badges"

Special Needs: "All current rank requirements for an advancement award (ranks, merit badges, or Eagle Palms) must actually be met by the candidate. There are no substitutions or alternatives permitted except those which are specifically stated in the requirements as set forth in the current official literature of the Boy Scouts of America." (quoted from BSA Advancement Policy #33088 p.40)

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