The BED file format is a standard format which was originally designed for listing annotation features, but which has also been widely used for large sets of mapped data.
Since the fields in a BED file are defined you will only see the common options when importing. The format doesn't support paired end reads so only single end options will be presented. You simply need to select the files you wish to import.
All BED files must define a chromosome, start and end position and these are all required by SeqMonk. There are many optional fields which can be included but the only one of these which will be used by SeqMonk is the strand field. All other fields will be ignored.