The first number represents the nitrogen percentage in your formula and the second represents the phosphate. The third is the Potash.
If you want primarily to provide nutrition during growth, you use one that is balanced or slightly higher in nitrogen. The new one you purchased is a bit higher in nitrogen than I usually see. Also, for orchids, you would use 1/2 to 1/4 strength weekly or biweekly. "Orchid specific" fertilizers are usually lower percentages. For example Dyna-grow is 7-9-5.
The first fertilizer you had was stronger in phosphorous and is used to boost blooms
You would apply this as your plant is finishing its new root and leaf growth and during a month or two prior to a rest period (if your plant is one with a rest period). Again, I would use probably 1/4 strength weekly or biweekly.
Hope that's helpful!