Set the multimeter to Ohms lowest scale. Place the probe tips together. The meter reading should be near zero, indicating little or no resistance.
Separate the probes and note the ohm reading goes very high (infinity). Infinity is extremely resistant to current flow. This is the stuff that makes lights not work.
When reading ohms, the meter supplies the power to measure circuits. So, the MC battery should be disconnected, so the circuit being tested has no outside power interference. (Old meters blow up if outside power is on the circuit under test). Anything you place the probe tips upon will receive power from the meter (it's very small). Place the probe tip an any wire, end to end and the meter will tell you if there is continuity through it. The lower the resistance the better, from an electrical flow standpoint.
Note the lines on the page of the wire diagram. Each one of those must be low resistance to make the circuit conduct power. Each device on the bike needs two connections to the battery terminals to draw power from it. Some devices can share these connections. You can place a probe at each end of any wire (represented by the wire diagram), and determine its electrical current carrying ability.
There is little danger to machine or human while testing circuits with a multimeter on the ohms scale. But, there is another way.
The meter can also read voltage if set to a voltage scale. (That's why they call it a multimeter, as it can have multiple functions depending on how the operator configures the device.) Use the DC voltage scale for the voltage you expect to see a reading. There are thousands of different multi-meters with slightly different control features. Since you didn't tell me what meter you have, I can only give general guidelines.
Anyway, assuming you have selected, say, a 20 VDC scale, place the probes against each other. Note the meter reading is zero, as the meter can detect no voltage in the circuit between the probe tips. Now place the probe tips on the battery terminals. Red to POS and Black to NEG. The meter should display the battery voltage potential. Note the reading.
With the battery connected to the bike, leave one probe on the battery neg terminal, and the red probe on each end of the fuse clips in turn. You should read the battery voltage at both terminals. If not there is a break in the path between the two clips. Guess what that could be?
You can "chase" the voltage through the bike wiring using the wire diagram to show where it should be distributed. As you follow, when voltage is not detected where it should be, go back to the last test connection where you did. Between those two points on the bike is a failed connection, which you will have to physically fix.
Remember, there are two connections to the battery for each device that uses power on the bike, even if it uses the frame as part of that connection path. If you find a voltage path to a lamp (for example) is intact, and the lamp still doesn't light, then there is probably that same voltage on the green side of the lamp connection (if the lamp is still good), and you follow the green path back to the battery negative until voltage is not found, go back to where last found and between those twp points is and open connection.
On the resistance scale, you can check for fuse continuity with the fuse removed from the bike. Set the meter to measure resistance and place the probe tips at either end. Infinaite resistance means a bad fuse, no or low resistance means the fuse is good.
During voltage checks, care must be taken with probe tip placement. If you short circuit a wire to the frame via the probe tip, you will blow a fuse, or smoke another wire as it draws maximum current from the battery during the short circuit. The heat and sparks generated can injure humans and the bike. So, watch it while testing a hot bike. Safety glasses may save your sight.
Go get 'em.
