The rules for this are detailed on page 62 of the D&D 3.5 Player's Handbook, under the heading "Acquiring Skills at 1st Level".
You receive (8 + Int modifier) x 4 skill points at level 1. The example used in the Player's Handbook is, conveniently for you, a halfling rogue with a +2 Int modifier who has 40 skill points to spend.
Each point you spend on a class skill (those listed as such in the rogue class description) gives one rank, with a maximum rank of 4 at first level, so it's convenient and beneficial to max out 10 class skills at 4 ranks each. This is in fact the officially recommended approach, as detailed in the halfling rogue starting package on page 51, and in my experience this is the preferred way among players. Pick any ten from the class skills list on page 50, but I most strongly recommend the recommended list on page 51.
- The five most important skills for a rogue are typically Hide, Move Silently, Disable Device, Open Lock, and Search. Spot and Listen are highly useful too.
- Among the worst skills are Forgery (I have never seen this used ever) and Profession (if you wanted to be a cobbler you wouldn't have become an adventurer).
Since cross-class skills cost two points per skill rank and have a lower maximum rank, it is generally not recommended to invest any skill points in those. However, your character may still find themself needing to use these skills at some point (e.g. you fall into water and need to use Swim untrained), so you should fill in all the skills on the character sheet anyway (you simply have zero ranks).
Even for trained-only skills, your character may find themself in a situation in which the DM specially allows them to use the skill untrained, such as a very easy check or a field the character is familiar with. It's not often important, but it does look tidy.