The Japanese speech system is very simple but also very limited and is unable to represent a lot of foreign sounds, like many of those in the English language. It's also important to note that English loan words like ベッド and ホット are NOT English words.

The loan words use the limited sounds of the Japanese system to approximate the English word, but you really should think of them as "only" inspired by the English words. Just like with any translation of a word, it might not have quite the same meaning in the other language, and Japanese people often do not understand the English version even when they're highly familiar with their loan version of it.

Japanese speech is based on "mora" with all the same length. In Japanese, each part of a-me-ri-ka takes the same amount of time, but in English there's stress on the "mer"-part. The small tsu っ/ッ is kind of like a pause, but your mouth is in a "holding pattern" to say the next mora.