Label eqMaxwell which will reference the main equation 11 above or adding a label at the end of each line before the command which will reference the sub-equation 11a or 11b above. Lots of good introductory material is included in the Short Math Guide for LaTeX. For example this equation would most likely span over two columns.
For example Emc2 will give Emc2.
Beginequation F F_x in F_c. Sometimes a long equation needs to be broken over multiple lines especially if using a double column export style. Limlimits_ x to infty exp -x 0. Lots of good introductory material is included in the Short Math Guide for LaTeX.