When a word is borrowed from one language to another, one of the problems that need solving is how to make the original sounds of the loanword fit into the new sound system. This has to do partly with the languages’ phonological inventories (i.e., which speech sounds they make use of), as well as their syllable structure (i.e., the language-specific restrictions on how consonants and vowels can be combined within a syllable).
If there are close matches for the individual sounds in the target language, this may not be a problem at all. For example, when Swedish borrowed the word cocktail from English, all that was needed to make it work phonologically was a slight tweaking of some sounds (primarily of the vowel qualities and the [l]-sound). The syllable structure of cocktail is also fully allowed in Swedish phonology.
In other cases, the task is more difficult. Finnish is a language that has many loanwords from Swedish, but notable phonological differences. For example, Finnish traditionally hasn’t allowed for initial consonant clusters (i.e., more than one consonant in the beginning of a word), which is why the Swedish word strand ‘beach’ lost two of the three initial consonants when it was borrowed into Finnish: ranta. This is an example of when a sound sequence in a loanword (3: [str]) is replaced with a smaller number of sounds (1: [r]).
But sometimes it can be difficult to find a 1-to-1 match between sounds, and in such cases, the opposite may happen: a sound in the source language can be replaced by a larger number of sounds in the target language. For example, the Swedish word biff ‘steak’ was borrowed into Finnish as pihvi. What’s going on here – why is [f] replaced by [hv]? Well, Finnish doesn’t have the [f]-sound, but it does have a [v]-sound, which is very similar: both are pronounced by a continuous airstream passing through a constriction between the upper teeth and the lower lip. In fact, the only difference between [f] and [v] is that [v] is voiced, which means that the vocal cords are vibrating (you can feel this yourself by pressing your fingers against your throat when pronouncing [f] and [v] alternatingly). However, the Finns must have felt that the [v]-sound didn’t quite do the job of replacing [f], so they threw in an [h] as well to get some of that sweet, voiceless flavour. Thus, the elements of a foreign sound can be split up and represented separately, if there isn’t a single sound that does the job to the speakers’ satisfaction.