Okay… well, you’ll need 3 things:
1). a MIDI trigger, such as a little keyboard that you hook up to your computer via USB… Just google “mini” “MIDI” and “trigger”, and you will get some very inexpensive little keyboards pop up.
2).a “softsynth”, which is a software-based synthesizer. Fortunately, nowadays there are many EXCELLENT free softsynths out there! Just google “free softsynth” and “pulse wave” and “strings”.
3). Ideally, you’ll want a DAW, which is a Digital Audio Workstation. A DAW is simply the “software environment” in which all sorts of digital music-making can take place, including the playing and sequencing of softsynths. There is an excellent free DAW out there called REAPER, which I highly recommend.
Do note that this DAW and this softsynth would’ve cost you MILLIONS OF DOLLARS in the 1980’s. Now they’re absolutely free!
During the time segments you indicated, what is most prominent is that melody, played on “high strings” in unison. My hunch is that the “strings” sonority is being produced by heavily chorused, poly-oscillator pulsed-waves, to which a tiny amount of very tight vibrato has been added, then given a good deal of reverb to make it sound “distant”.
The riff being played is based on A Aeolian mode, or so-called A “natural minor”.