‘And when he entered again into Capernaum after some days the news went round about him that (literally ‘ he was heard that --') he was in the house, and many were gathered together so that there was no longer room for them, no, not even about the door. And he spoke the word to them.'
After a period of ministry around the towns of Galilee Jesus went back to Peter's home for a rest. But the news was soon passed around that He had come and was in ‘the house' which was their temporary headquarters in Galilee. The result was that the crowds gathered, and they pressed in on the house so that there was not even space around the door. The eyewitness remembers the scene clearly. It would seem that normally they would expect the crowds to leave a decent space by the door.
The door would be open, as it was daytime, and in view of what follows we can presume that Jesus was speaking to the crowds from within the house (compare how He later uses a boat in order to prevent being hemmed in by the crowds).
‘And he spoke the word to them.' Mark (or his source) wants us to recognise that this was His purpose in coming, so that the people might hear ‘the word' that He had brought to them from God. The sower sows the word.
The end result of all this was that when four men came bringing a paralysed man on a mattress they could not approach the door and get him to Jesus.