This process was sometimes called linkage editing and the output known as a load module. A compiler works with what are sometimes called 3GL and higher-level languages. An assembler works on programs written using a processor's assembler language.
In general, however, when between vowels (as in exactamente) the Spanish x is pronounced like the English ks sound but softer or less explosive. When it comes before another consonant (as in expediciÃ³n), it has the s sound in some regions/countries but the soft ks sound in others.
If you refer to the Spanish for and, then the rule is to use e if the following word begins with the sound of i (which may be spelled hi or y). There is a similar rule about or which is normally o but is changed to u if the following word begins with ho or o.