In Japanese, describing things that can be experienced with the senses (excluding visual), is a little bit different to the way that we would convey it in English. Traditionally, we would use unique verbs for each of these situations, such as ‘smells like (A)’, ‘tastes like (A)’, ‘feels like (A)’, etc. While this is still possible in Japanese, it is not the most common way.
がする is a grammar construction that focuses on the source of the smell, sound, taste, or feeling, and makes the sensory experience itself the subject of the sentence. To use
がする, simply attach it to the end of any phrase that expresses which type of ‘sense’ is being created/given off by the subject.
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この石鹸（せっけん）はバラの匂（にお）いがするから好（す）きです。
I like this soap because it smells like roses. (Literally, ‘it gives off a rose smell’)
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誰（だれ）かが階段（かいだん）を上（あ）がっている音（おと）がする。
I hear someone coming up the stairs. (Literally, ‘the sound of someone coming up the stairs is being made’)
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このバナナが変（へん）な味（あじ）がする。
This banana tastes weird. (Literally, ‘it gives off a strange flavor’)
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誰（だれ）かに見（み）られている感（かん）じがする。
It feels like I'm being watched by someone. (Literally, ‘the feeling of being watched is happening’)
Japanese often uses 気（き） ‘energy’, ‘spirit’, as something that can be perceived with the senses. Due to this, there are many phrases which use
～気（き）がする in the same way as this grammar point.
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ヤバい、鍵（かぎ）をかけるのを忘（わす）れた気（き）がする。
Shoot, I feel like I forgot to lock my door. (Literally, ‘my attention is being drawn to that I may have forgotten to lock the door’)
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なんか忘（わす）れた気（き）がする。
I feel like I forgot something. (Literally, ‘my attention is being drawn to that something was forgotten’)