Charles Bennett wrote:Without information it is almost impossible to help.
What version of Resolve, and is it Free or Studio? What OS, amount of RAM, and GPU are you using? What is the source, resolution, and codec used for your video clips?
You can never give too much information when asking for help on the forum.

I'm using Davinci Resolve 18.1.2 free version.
Computer: MSI MS-7B85
CPU: AMD Ryzen 7 2700X (Pinnacle Ridge, PiR-B2)
3700 MHz (37.00x100.0) @ 4200 MHz (42.00x100.0)
Motherboard: MSI B450 GAMING PRO CARBON AC (MS-7B85)
BIOS: 1.C0, 06/11/2020
Chipset: AMD B450 (Low-Power Promontory PROM26.A)
Memory: 16384 MBytes @ 1600 MHz, 16-18-18-36
- 8192 MB PC25600 DDR4 SDRAM - Patriot Memory (PDP Systems) 3200 C16 Series
- 8192 MB PC25600 DDR4 SDRAM - Patriot Memory (PDP Systems) 3200 C16 Series
Graphics: ASUS DUAL GTX 1070 OC
NVIDIA GeForce GTX 1070, 8192 MB GDDR5 SDRAM
Drive: WDC WD10EZEX-08WN4A0, 976.8 GB, Serial ATA 6Gb/s @ 6Gb/s
Drive: Samsung SSD 850 EVO 500GB, 488.4 GB, Serial ATA 6Gb/s @ 6Gb/s
Drive: WDC WD10EZEX-08M2NA0, 976.8 GB, Serial ATA 6Gb/s @ 6Gb/s
Sound: NVIDIA GP104 - High Definition Audio Controller
Sound: AMD Zen - HD Audio Controller
Network: Intel Wireless-AC 9260 160MHz
Network: Intel I211AT Copper (Pearsonville) Network Adapter
OS: Microsoft Windows 10 Home (x64) Build 19045.2486