SSD read/writes are WAY faster then a HDD. a HDD is a mechanical device with a physical spinning disk. When you try to access the disk much spin to location where the file is so the read/write head can get to it. if the file is fragmented the disk will need to spin even more, this process is sometimes called "seeking". In compassion a SSD is all electrical reading bits from flash storage memory cells with no or little "seeking" time. Search from youtube videos to see the different SSD vs HDD speed text. or SSD vs 5400RPM HDD vs 7200RPM HDD.
SSD are well worth the price. get a 128GB~ SDD, for you OS if you want more storage buy a 1TB HDD.