Well first the ones you asked for:
GHz: The clock speed of a processor. A 1GHz CPU has a cycle every nanosecond. Comparing clock speed is only useful when comparing between same family CPUs, e.g. an FX-8320E has a slower clock speed than the FX-9590 and is slower, but an i7-5920 has a slower clock speed but performs better. Some people overclock to gain extra performance but this requires more power and thus better cooling. GPUs also have clock speeds but they are even fuzzier, but RAM is very similar though.
Ti: A term used by NVIDIA to describe a more powerful model of a same number GPU. An example is the GTX 750 Ti, which is better than the GTX 750. The equivalent AMD extension is X, so an R9 280 does worse than an R9 280X.
CPU...