You need to start with a good seed raising mix, this has the right fertiliser in it for seeds, reasonable quick and not too strong. It is important to use this instead of a potting mix which has a 6 month slow release fertiliser in it, not quick enough for raising seeds.
Start with a suitable tray/container with drainage in the bottom, 3/4 fill with mix and firm down evenly, scatter seeds evenly them , try not to clump, then lightly cover with seedmix. Water then place in a warm sunny spot to germinate, keep moist. You can also buy small plastic covered trays to keep seeds moist and warm.
As soon as seeds germinate don't let them get too leggy. When old enough to handle "prick" them out into separate punnets to grow on ready for outside planting.
You can purchase jiffy or peat pots that you can put in individual seeds. For single plants or a few seeds for the likes of silverbeets etc that don't have to be separated. The jiffy range comes flat and when wet swell, then you can see where the seeds are placed in the centre, you don't require any mixes with these. Peat pots you fill with seed raising mix, plant the seed, then water well.
Keep moist and warm and when seeds germinate you don't have to repot but continue growing and then harden off first before planting outside. Sowing seed to harvesting - a very rewarding process.