They will put the picture on the left, the first line of text next to it and all the following text below the picture. This text is next to the apple and continues below it. This text is next to the apple and continues below it. Normally, browsers will put the images and text right next to eachother. If you use style sheets , you can define white space around the image separately for each of the 4 sides as well as the padding between the image and the border.
Some browsers support the height and width attributes.
That means that in the link to the image the size is included. The advantage of this is that the browser can download all of the text of a page and do the lay-out, before downloading the images. In practice this means that the user can start reading the text while the pictures are still being downloaded. You can use a drawing or graphics programme to get the size of the images you use. Many HTML editors can insert width and height automatically.