This is not as straightforward as you might think and the process of moving from contigs to a draft genome is difficult. This can vary on the type of organism, the size of the genome, the frequency of gene space, the depth of sequencing, etc. You didn't give us any of this information so it's hard to guide you. There are numerous ways to close contigs or scaffolds but much of this depends on how similar your sequenced contigs are to those from already sequenced genomes.
If you have a relatively small genome (bacterial or very small eukaryote less than ~40Mb), I have had good luck using the PAGIT pipeline (Post Assembly Genome Improvement Tool) (see these links for the pipeline and paper). This pipeline (as well as others like this) require a lot of memory, so you won't be able to do this on a laptop or desktop computer.